U.S. patent application number 16/531280 was filed with the patent office on 2019-11-28 for thermal barrier coating repair compositions and methods of use thereof.
The applicant listed for this patent is General Electric Company. Invention is credited to Susan Corah, Hrishikesh Keshavan, Kevin Paul McEvoy, James Ruud, Atanu Saha, Lawrence E. Szala.
Application Number | 20190359528 16/531280 |
Document ID | / |
Family ID | 59762053 |
Filed Date | 2019-11-28 |
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United States Patent
Application |
20190359528 |
Kind Code |
A1 |
McEvoy; Kevin Paul ; et
al. |
November 28, 2019 |
THERMAL BARRIER COATING REPAIR COMPOSITIONS AND METHODS OF USE
THEREOF
Abstract
The present inventive subject matter is directed to repair
compositions for thermal barrier coatings and methods of use
thereof. The repair compositions include a ceramic composition, a
colloidal solution, an aqueous binder, an aqueous dispersant, and
an aqueous ammonia solution. The ceramic composition includes a
first population of yttria-stabilized zirconia particles having a
mean diameter from about 250 nm to about 1000 nm, a second
population of yttria-stabilized zirconia particles having a mean
diameter from about 2 .mu.m to about 10 .mu.m, and a third
population of yttria-stabilized zirconia particles having a mean
diameter from about 20 .mu.m to about 250 .mu.m. One method
includes depositing the repair layer onto the damaged region, the
repair layer including the repair composition, and heat treating
the repair layer.
Inventors: |
McEvoy; Kevin Paul;
(Fairborn, OH) ; Ruud; James; (Delmar, NY)
; Szala; Lawrence E.; (Scotia, NY) ; Corah;
Susan; (Glenville, NY) ; Saha; Atanu;
(Bangalore, IN) ; Keshavan; Hrishikesh;
(Watervliet, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
General Electric Company |
Schenectady |
NY |
US |
|
|
Family ID: |
59762053 |
Appl. No.: |
16/531280 |
Filed: |
August 5, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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15243005 |
Aug 22, 2016 |
10384978 |
|
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16531280 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F05B 2230/90 20130101;
F05B 2230/80 20130101; F05D 2300/2118 20130101; C04B 2235/9607
20130101; F01D 5/288 20130101; Y02T 50/6765 20180501; C23C 4/134
20160101; C04B 35/64 20130101; C04B 35/48 20130101; C04B 41/5042
20130101; C23C 14/221 20130101; C04B 2235/5436 20130101; Y02T 50/60
20130101; C23C 4/11 20160101; C04B 2235/5445 20130101; F01D 5/005
20130101; C04B 41/87 20130101; C04B 35/62222 20130101; C23C 28/3455
20130101; F05C 2203/0895 20130101; C04B 41/009 20130101; C04B
41/009 20130101; C04B 35/48 20130101; C04B 41/5042 20130101; C04B
41/4539 20130101; C04B 41/4547 20130101 |
International
Class: |
C04B 35/48 20060101
C04B035/48; C23C 28/00 20060101 C23C028/00; F01D 5/00 20060101
F01D005/00; F01D 5/28 20060101 F01D005/28; C04B 35/622 20060101
C04B035/622; C04B 35/64 20060101 C04B035/64; C04B 41/87 20060101
C04B041/87; C04B 41/50 20060101 C04B041/50; C23C 14/22 20060101
C23C014/22; C23C 4/134 20060101 C23C004/134; C23C 4/11 20060101
C23C004/11; C04B 41/00 20060101 C04B041/00 |
Claims
1. A repair composition comprising: a ceramic composition in an
amount of from about 40 to about 60 percent by volume of the repair
composition; a colloidal solution in an amount of from about 15 to
about 25 percent by volume of the repair composition; an aqueous
binder in an amount of from about 5 to about 15 percent by volume
of the repair composition; an aqueous dispersant in an amount of
from about 4 to about 8 percent by volume of the repair
composition; and an aqueous ammonia solution in an amount of from
about 5 to about 10 percent by volume of the repair composition;
wherein the ceramic composition comprises: a first population of
yttria-stabilized zirconia particles having a mean diameter from
about 250 nm to about 1000 nm, in an amount of from about 15 to
about 30 percent by volume of the ceramic composition; a second
population of yttria-stabilized zirconia particles having a mean
diameter from about 2 .mu.m to about 10 .mu.m, in an amount of from
about 10 to about 25 percent by volume of the ceramic composition;
and a third population of yttria-stabilized zirconia particles
having a mean diameter from about 20 .mu.m to about 250 .mu.m, in
an amount of from about 50 to about 70 percent by volume of the
ceramic composition; and wherein the colloidal solution comprises:
an aqueous solvent in an amount of from about 90 to about 98
percent by volume of the colloidal solution; and a fourth
population of yttria-stabilized zirconia particles having a mean
diameter from about 2 nm to about 200 nm, in an amount of from
about 2 to about 10 percent by volume of the colloidal
solution.
2. The repair composition of claim 1, wherein the repair
composition does not include silicone, silica, or silicate.
3. The repair composition of claim 1, wherein the first population
of yttria-stabilized zirconia particles, the second population of
yttria-stabilized zirconia particles, the third population of
yttria-stabilized zirconia particles, and the fourth population of
yttria-stabilized zirconia particles have from about 4 to about 60
mole percent yttrium oxide content.
4. The repair composition of claim 1, wherein the aqueous binder
comprises water and a binder selected from the group consisting of
poly(alkylene carbonate) copolymer, cellulose binder, poly(vinyl
alcohol), and polyethylene glycol.
5. The repair composition of claim 1, wherein the aqueous
dispersant comprises ammonium polyacrylate and water.
6. The repair composition of claim 1, wherein the aqueous ammonia
solution comprises ammonia and water, wherein the ammonia is in an
amount of from about 25 to about 50 percent by volume of the
aqueous ammonia solution.
7. The repair composition of claim 1, wherein the ceramic
composition is in an amount of from about 45 to about 55 percent by
volume of the repair composition; the colloidal solution is in an
amount of from about 18 to about 22 percent by volume of the repair
composition; the aqueous binder is in an amount of from about 10 to
about 15 percent by volume of the repair composition; the aqueous
dispersant is in an amount of from about 6 to about 8 percent by
volume of the repair composition; and the aqueous ammonia solution
is in an amount of from about 8 to about 10 percent by volume of
the repair composition.
8. The repair composition of claim 1, wherein the first population
of yttria-stabilized zirconia particles is in an amount of from
about 22 to about 28 percent by volume of the ceramic composition;
the second population of yttria-stabilized zirconia particles is in
an amount of from about 15 to about 20 percent by volume of the
ceramic composition; and the third population of yttria-stabilized
zirconia particles is in an amount of from about 55 to about 65
percent by volume of the ceramic composition.
9. The repair composition of claim 1, wherein the first population
of yttria-stabilized zirconia particles is in an amount of about 15
percent by volume of the repair composition; the second population
of yttria-stabilized zirconia particles is in an amount of about 10
percent by volume of the repair composition; and the third
population of yttria-stabilized zirconia particles is in an amount
of about 30 percent by volume of the repair composition.
10. The repair composition of claim 9, wherein the colloidal
solution is in an amount of about 20 percent by volume of the
repair composition; the aqueous binder is in an amount of about 10
percent by volume of the repair composition; the aqueous dispersant
is in an amount of about 6 percent by volume of the repair
composition; and the aqueous ammonia solution is in an amount of
about 9 percent by volume of the repair composition.
11. A repair composition comprising: a ceramic composition in an
amount of from about 40 to about 60 percent by volume of the repair
composition; a colloidal solution in an amount of from about 15 to
about 25 percent by volume of the repair composition; an aqueous
binder in an amount of from about 5 to about 15 percent by volume
of the repair composition; an aqueous dispersant in an amount of
from about 4 to about 8 percent by volume of the repair
composition; and an aqueous ammonia solution in an amount of from
about 5 to about 10 percent by volume of the repair composition;
wherein the ceramic composition comprises: a first population of
yttria-stabilized zirconia particles having a mean diameter from
about 250 nm to about 1000 nm; a second population of
yttria-stabilized zirconia particles having a mean diameter from
about 2 .mu.m to about 10 .mu.m; and a third population of
yttria-stabilized zirconia particles having a mean diameter from
about 20 .mu.m to about 250 .mu.m; and wherein the colloidal
solution comprises: an aqueous solvent in an amount of from about
90 to about 98 percent by volume of the colloidal solution; and a
fourth population of yttria-stabilized zirconia particles having a
mean diameter from about 2 nm to about 200 nm.
12. The repair composition of claim 11, wherein the first
population of yttria-stabilized zirconia particles is in an amount
of from about 15 to about 30 percent by volume of the ceramic
composition.
13. The repair composition of claim 11, wherein the second
population of yttria-stabilized zirconia particles is in an amount
of from about 10 to about 25 percent by volume of the ceramic
composition.
14. The repair composition of claim 11, wherein the third
population of yttria-stabilized zirconia particles is in an amount
of from about 50 to about 70 percent by volume of the ceramic
composition.
15. The repair composition of claim 11, wherein the fourth
population of yttria-stabilized zirconia particles is in an amount
of from about 2 to about 10 percent by volume of the colloidal
solution.
16. The repair composition of claim 11, wherein the first, second,
third, and fourth populations of yttria-stabilized zirconia
particles have from about 4 to about 20 mole percent yttrium oxide
content
17. The repair composition of claim 11, wherein the aqueous binder
includes polypropylene carbonate and water.
18. The repair composition of claim 11, wherein the aqueous
dispersant includes ammonium polyacrylate and water.
19. The repair composition of claim 11, wherein the aqueous ammonia
solution includes ammonia and water, and the ammonia is in an
amount of from about 25 to about 50 percent by volume of the
aqueous ammonia solution.
20. The repair composition of claim 11, wherein the mean diameter
of the first population of yttria-stabilized zirconia particles is
about 800 nm; the mean diameter of the second population of
yttria-stabilized zirconia particles is about 4 .mu.m; and the mean
diameter of the third population of yttria-stabilized zirconia
particles is about 25 .mu.m.
21. A repair composition comprising: a ceramic composition
including a first population of yttria-stabilized zirconia
particles, a second population of yttria-stabilized zirconia
particles, and a third population of yttria-stabilized zirconia
particles, wherein the first population has a mean diameter from
about 250 nm to about 1000 nm, the second population has a mean
diameter from about 2 .mu.m to about 10 .mu.m, and the third
population has a mean diameter from about 20 .mu.m to about 250
.mu.m; a colloidal solution including an aqueous solvent and a
fourth population of yttria-stabilized zirconia particles, the
fourth population having a mean diameter from about 2 nm to about
200 nm; an aqueous binder; an aqueous dispersant; and an aqueous
ammonia solution.
22. The repair composition of claim 21, wherein the ceramic
composition is in an amount of from about 40 to about 60 percent by
volume of the repair composition.
23. The repair composition of claim 21, wherein the colloidal
solution in an amount of from about 15 to about 25 percent by
volume of the repair composition, and the aqueous solvent is in an
amount of from about 90 to about 98 percent by volume of the
colloidal solution.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 15/243,005, filed Aug. 22, 2016, and the entire disclosure of
which is incorporated by reference herein.
FIELD
[0002] The present disclosure is directed to repair compositions
for repairing damaged areas of thermal barrier coatings and methods
of use thereof.
BACKGROUND
[0003] Higher operating temperatures of gas turbine engines are
continually being sought in order to increase the efficiency of the
engines. However, as operating temperatures increase, the high
temperature durability of the components of the engine must
correspondingly increase. Significant advances in high temperature
capabilities have been achieved through the formulation of nickel,
cobalt and iron-based superalloys. These superalloys can be
designed to withstand temperatures in the range of about 1000 to
about 1100.degree. C. or higher. Nonetheless, when used to form
components of the turbine, such as combustor liners, augmentor
hardware, shrouds and high and low-pressure nozzles and blades, the
superalloys alone could be susceptible to damage by oxidation and
hot corrosion attack. Accordingly, these components are typically
protected by an environmental and/or a thermal barrier coating
(TBC). In general, TBCs can be used in conjunction with the
superalloys in order to reduce the cooling air requirements
associated with a given turbine. Ceramic materials, such as
yttrium-stabilized zirconia (YSZ), are widely used as a TBC or
topcoat of TBC systems. These materials are employed because, for
example, they can be readily deposited by plasma-spraying and
physical vapor deposition (PVD) techniques, and they also generally
exhibit desirable thermal characteristics. In general, these TBCs
can be utilized in conjunction with the superalloys in order to
reduce the cooling air requirements associated with a given
turbine.
[0004] In order to be effective, TBCs need to possess low thermal
conductivity, strongly adhere to the component and remain adhered
through many heating and cooling cycles. The latter requirement is
particularly demanding due to the different coefficients of thermal
expansion between the ceramic materials and the superalloy
substrates that they protect. To promote adhesion and extend the
service life of a TBC, an oxidation-resistant bond coating
typically takes the form of a diffusion aluminide coating or an
overlay coating, such as MCrAlX where M is iron, cobalt and/or
nickel and X is yttrium or another rare earth element. During the
deposition of a ceramic TBC and subsequent exposures to high
temperatures, such as during engine operation, these bond coats
form a tightly adherent alumina (Al.sub.2O.sub.3) layer or scale
that adheres the TBC to the bond coat.
[0005] The service life of a TBC is typically limited by a
spallation event brought on by, for example, thermal fatigue.
Accordingly, a significant challenge has been to obtain a more
adherent ceramic layer that is less susceptible to spalling when
subjected to thermal cycling. Though significant advances have been
made, there is the inevitable requirement to repair components
whose thermal barrier coatings have spalled. Though spallation
typically occurs in localized regions or patches, a conventional
repair method has been to completely remove the TBC after removing
the affected component from the turbine or other area, restore or
repair the bond coat as necessary and recoat the engine component.
Techniques for removing TBCs include grit blasting or chemically
stripping with an alkaline solution at high temperatures and
pressures. However, grit blasting is a slow, labor-intensive
process and can erode the surface beneath the coating. The use of
an alkaline solution to remove a TBC also is less than ideal
because the process typically requires the use of an autoclave
operating at high temperatures and pressures. Consequently, some
conventional repair methods are labor intensive and expensive, and
can be difficult to perform on components with complex geometries,
such as airfoils and shrouds. As an alternative, U.S. Pat. No.
5,723,078 to Nagaraj et al. teach selectively repairing a spalled
region of a TBC by texturing the exposed surface of the bond coat,
and then depositing a ceramic material on the textured surface by
plasma spraying. While avoiding the necessity to strip the entire
TBC from a component, the repair method taught by Nagaraj et al.
requires removal of the component in order to deposit the ceramic
material.
[0006] In the case of large power generation turbines, completely
halting power generation for an extended period of time in order to
remove components whose TBCs have suffered only localized
spallation is not economically desirable.
[0007] U.S. Pat. No. 7,476,703 to Ruud et al. discloses an in-situ
method and composition for repairing a thermal barrier coating,
which is based on a silicone resin system. While this in-situ
method alleviates the disassembly, masking and over-spraying
problems associated with some conventional TBC repair methods, it
is not an ideal repair for large area defects (i.e., defects that
are greater than 1 square inch in size). U.S. Pat. No. 6,413,578 to
Stowell et al. discloses an in-situ method for repairing thermal
barrier coating with a ceramic paste. However, this method uses a
repair composition that contains ethyl alcohol. As a result,
flammable ethyl alcohol fumes are released when the repair
composition is used, which creates environmental health and safety
risks.
[0008] A commercially available repair composition, AIM-MRO SR
Resin Patch, may be used for TBC repair. However, this repair
composition is silicate based and for this reason does not offer
the desired performance of thermal barrier coating. Additionally,
the commercial repair composition cannot be used to repair large
area defects, such as when the damaged area is greater than 1
square inch in size.
[0009] Accordingly, despite the above advances, it would be
desirable if a repair method and a repair composition were
available that could be performed on damaged regions of various
sizes, including large damaged regions (i.e., damaged regions that
are greater than 1 square inch in size), without necessitating that
the component be removed from the turbine, so that downtime and
scrappage are minimized. Such damaged regions may be created by
localized spallation, damage caused by tool hits, and/or chipping.
Furthermore, it would be desirable to have a repair composition
that uses water as a liquid carrier, thus avoiding environmental
health and safety risks associated with repair compositions that
use organic solvents, such as ethyl alcohol.
SUMMARY
[0010] The present inventive subject matter relates to repair
compositions for thermal barrier coating and methods of use of the
disclosed repair compositions. Thus, in one embodiment, a repair
composition is provided that includes: a ceramic composition in an
amount of from about 40 to about 60 percent by volume of the repair
composition; a colloidal solution in an amount of from about 15 to
about 25 percent by volume of the repair composition; an aqueous
binder in an amount of from about 5 to about 15 percent by volume
of the repair composition; an aqueous dispersant in an amount of
from about 4 to about 8 percent by volume of the repair
composition; and an aqueous ammonia solution in an amount of from
about 5 to about 15 percent, for example, 9 percent, by volume of
the repair composition.
[0011] The ceramic composition includes: a first population of
yttria-stabilized zirconia particles having a mean diameter from
about 250 nm to about 1000 nm, in an amount of from about 15 to
about 30 percent by volume of the ceramic composition; a second
population of yttria-stabilized zirconia particles having a mean
diameter from about 2 .mu.m to about 10 .mu.m, in an amount of from
about 10 to about 25 percent by volume of the ceramic composition;
and a third population of yttria-stabilized zirconia particles
having a mean diameter from about 20 .mu.m to about 250 .mu.m, in
an amount of from about 50 to about 70 percent by volume of the
ceramic composition.
[0012] The colloidal solution includes: an aqueous solvent in an
amount of from about 90 to about 98 percent by volume of the
colloidal solution; and a fourth population of yttria-stabilized
zirconia particles having a mean diameter from about 2 nm to about
200 nm, in an amount of from about 2 to about 10 percent by volume
of the colloidal solution.
[0013] In another embodiment, the invention is directed to a method
for repairing a thermal barrier coating, wherein the thermal
barrier coating is located on a component and wherein the thermal
barrier coating has a damaged region, the method including:
depositing a repair layer onto the damaged region, the repair layer
including the disclosed herein repair composition; and heat
treating the repair layer at a temperature of from about
900.degree. C. to about 1400.degree. C., to thereby form a
patch.
[0014] In another embodiment, a method for repairing a thermal
barrier coating is provided. The thermal barrier coating is located
on a component and wherein the thermal barrier coating has a
damaged region, the method including: depositing an initial layer
onto the damaged area, the initial layer including the described
herein repair composition; heat treating the initial layer at a
temperature of from about 250.degree. C. to about 600.degree. C.;
optionally, repeating one or more times a combination of the steps
of depositing the initial layer onto the damaged area and heat
treating the initial layer at a temperature of from about
250.degree. C. to about 600.degree. C., to thereby form a plurality
of initial layers; depositing a final layer onto the initial layer
or onto the plurality of initial layers, the final layer including
the disclosed herein repair composition; and concurrently heat
treating the final layer and the initial layer at a temperature of
from about 900.degree. C. to about 1400.degree. C., to thereby form
a patch; or concurrently heat treating the final layer and the
plurality of initial layers at a temperature of from about
900.degree. C. to about 1400.degree. C., to thereby form the
patch.
[0015] The repair compositions and methods disclosed herein have
numerous advantages. The disclosed repair composition and methods
could be used to repair damaged regions of various sizes, including
large damaged regions that are greater than 1 square inch in size.
Our repair compositions use water as a liquid carrier, thus
avoiding environmental health and safety risks associated with
repair compositions that use organic solvents, such as ethyl
alcohol.
[0016] Furthermore, the disclosed repair compositions are a
thixotropic (i.e., shear thinning) slurry system, which enables one
to use the disclosed repair compositions to deposit a near net
shape patch. The disclosed herein repair compositions retain near
net shape through our unique design of particle distribution,
optimization of solids loading, and sol (i.e., colloidal solution)
chemistry.
[0017] Moreover, the methods disclosed herein are advantageous
because they can be performed in situ, without dismantling or
removing components that need to be repaired. The repaired TBC can
then be sintered at temperatures lower than engine operating
temperature without any dimensional instability. Not having to
dismantle and remove components for stripping and recoating makes
our disclosed herein methods less laborious, very cost effective,
and affording a drastic reduction in the down time of an engine.
Additionally, our methods do not require any additional sintering
cycles to sinter the repair composition before it undergoes service
cycles.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] These and other features, aspects, and advantages of the
inventive subject matter will become better understood when the
following detailed description is read with reference to the
accompanying drawings in which like characters represent like parts
throughout the drawings, wherein:
[0019] FIG. 1 provides an idealized cross-sectional view of the
thermal barrier coating, the component, and the damaged region.
[0020] FIG. 2 provides an idealized cross-sectional view of the
thermal barrier coating, the component, and the repair layer.
[0021] FIG. 3 provides an idealized cross-sectional view of the
thermal barrier coating, the component, the initial layer, and the
final layer.
DETAILED DESCRIPTION
[0022] In the following specification and the claims which follow,
reference will be made to a number of terms, which shall be defined
to have the following meanings.
[0023] The singular forms "a", "an", and "the" include plural
referents unless the context clearly dictates otherwise.
[0024] Approximating language, as used herein throughout the
specification and claims, may be applied to modify any quantitative
representation that could permissibly vary without resulting in a
change in the basic function to which it is related. Accordingly, a
value modified by a term or terms, such as "about", is not to be
limited to the precise value specified. In some instances, the
approximating language may correspond to the precision of an
instrument for measuring the value.
[0025] As used herein, the term "colloidal solution" refers to a
solution in which particles are evenly suspended in a liquid. These
particles are sufficiently fine in size so that the suspension is
stable and there is no sedimentation of particles from the
suspension.
[0026] As used herein, the term "yttria-stabilized zirconia" refers
to a ceramic in which the crystal structure of zirconium dioxide,
i.e., "zirconia" (ZrO.sub.2), has an addition of yttrium oxide,
i.e., "yttria" (Y.sub.2O.sub.3).
[0027] As used herein, the term "thermal barrier coating" is known
in the art and refers to materials systems usually applied to
metallic surfaces, such as on gas turbine or aero-engine parts,
operating at elevated temperatures, as a form of exhaust heat
management.
[0028] As used herein, the term "mil" refers to unit of measurement
equal to a thousandth of an inch, i.e., 0.001 inches or 25.40
.mu.m. A plural form of "mil" is "mils".
[0029] A mean diameter of particles (i.e., d50) may be measured by
laser diffraction technique in a MASTERSIZER 3000.TM. laser
diffraction particle size analyzer manufactured by Malvern
Instrument Ltd.
[0030] In one embodiment, a repair composition is provided that
includes: a ceramic composition in an amount of from about 40 to
about 60 percent by volume of the repair composition; a colloidal
solution in an amount of from about 15 to about 25 percent by
volume of the repair composition; an aqueous binder in an amount of
from about 5 to about 15 percent by volume of the repair
composition; an aqueous dispersant in an amount of from about 4 to
about 8 percent by volume of the repair composition; and an aqueous
ammonia solution in an amount of from about 5 to about 10 percent
by volume of the repair composition.
[0031] In one embodiment, the ceramic composition is in an amount
of from about 45 to about 55 percent by volume of the repair
composition. In one embodiment, the colloidal solution is in an
amount of from about 18 to about 22 percent by volume of the repair
composition. In one embodiment, the aqueous binder is in an amount
of from about 10 to about 15 percent by volume of the repair
composition. In one embodiment, the aqueous dispersant is in an
amount of from about 6 to about 8 percent by volume of the repair
composition. In one embodiment, the aqueous ammonia solution is in
an amount of from about 8 to about 10 percent by volume of the
repair composition.
[0032] The ceramic composition includes: a first population of
yttria-stabilized zirconia particles having a mean diameter from
about 250 nm to about 1000 nm (i.e., fine particles population), in
an amount of from about 15 to about 30 percent by volume of the
ceramic composition; a second population of yttria-stabilized
zirconia particles having a mean diameter from about 2 .mu.m to
about 10 .mu.m (i.e., medium particles population), in an amount of
from about 10 to about 25 percent by volume of the ceramic
composition; and a third population of yttria-stabilized zirconia
particles having a mean diameter from about 20 .mu.m to about 250
.mu.m (i.e., coarse particles population), in an amount of from
about 50 to about 70 percent by volume of the ceramic
composition.
[0033] In one embodiment, the first population of yttria-stabilized
zirconia particles is in an amount of from about 22 to about 28
percent by volume of the ceramic composition. In one embodiment,
the second population of yttria-stabilized zirconia particles is in
an amount of from about 15 to about 20 percent by volume of the
ceramic composition. In one embodiment, the third population of
yttria-stabilized zirconia particles is in an amount of from about
55 to about 65 percent by volume of the ceramic composition. The
approximating term "about" refers to the precision of an instrument
for measuring the value.
[0034] The ceramic composition includes a mixture of various
particle size classes, including a coarse size class (i.e., third
population of yttria-stabilized zirconia particles), a medium size
class (i.e., second population of yttria-stabilized zirconia
particles), and a fine size class (i.e., first population of
yttria-stabilized zirconia particles). The absolute size and
relative proportions of the particles selected for each class
depend in large part on the desired final thickness of the coating
being repaired. For example, the coarse size class (that is, the
largest particle class used in the ceramic composition) is selected
to build coating volume to the desired thickness, and as such can
be thought of as being used as a scaffold for the repaired coating.
The medium size class, then, is selected to fill in the bulk of the
interstitial space between particles of the coarse size class; the
other particle size classes are similarly selected to fill in
remaining interstitial space. By carefully selecting the size and
relative proportions of the various size classes, a coating of a
desired thickness can be fabricated with much higher density than
can be achieved by building a coating from a single size class.
[0035] The coarse size class, then, is selected based in large part
on the desired thickness of the resultant coating, and in some
embodiments has a median particle size in the range from about 20
.mu.m to about 250 .mu.m. In applications where comparatively thin
coatings are used, the median particle size range for the coarse
size class may be smaller, such as from about 20 .mu.m to about 50
.mu.m. In applications where comparatively thick coatings are used,
the median particle size range for the coarse size class may be
larger, such as from about 30 .mu.m to about 250 .mu.m. Typically,
the coarse size class particles make up from about 50 percent to
about 70 percent of the volume of the ceramic composition.
[0036] The smaller size classes are then selected to reinforce the
scaffold created by the coarse size class as noted above. In some
embodiments, the medium size class has a median particle size in
the range from about 2 .mu.m to about 10 .mu.m. In applications
employing comparatively thin coatings, the median particle size
range may be smaller, such as from about 2 .mu.m to about 6 .mu.m.
In applications employing comparatively thicker coatings, the
median particle size range may be larger, such as from about 5
.mu.m to about 10 .mu.m. Typically, the medium size class particles
make up from about 10 percent to about 25 percent of the volume of
the ceramic composition. In some embodiments, the fine size class
has a median particle size in the range from about 250 nm to about
1 .mu.m. In some embodiments, depending on the size of the voids
intended to be filled by the fine particle size class, the median
particle size of the fine size class is in a range from about 500
nm to about 1 .mu.m. Typically, the fine size class particles make
up from about 15 percent to about 30 percent of the volume of the
ceramic composition.
[0037] A commercially available suitable first population of
yttria-stabilized zirconia particles (fine particles) is available
under the name TOSOH-4Y from TOSOH USA Inc. A commercially
available suitable second population of yttria-stabilized zirconia
particles (medium particles) is available under the name Imerys
8YSZ-HP 5 .mu.m from Imerys Fused Minerals. A commercially
available suitable third population of yttria-stabilized zirconia
particles (large particles) is available under the name Amperit 825
from HC Stark GmBH.
[0038] The colloidal solution includes: an aqueous solvent in an
amount of from about 90 to about 98 percent by volume of the
colloidal solution; and a fourth population of yttria-stabilized
zirconia particles having particles with a mean diameter from about
2 nm to about 200 nm (i.e., very fine particles population), in an
amount of from about 2 to about 10 percent by volume of the
colloidal solution.
[0039] In one embodiment, the aqueous solvent of the colloidal
solution is in an amount of from about 92 to about 98 percent by
volume of the colloidal solution and the fourth population of
yttria-stabilized zirconia particles is in an amount of from about
2 to about 8 percent by volume of the colloidal solution. A
commercially available suitable colloidal solution is available
under the name ZRYS4 from Nyacol Nano Technologies.
[0040] In one embodiment, the repair composition does not include
silicone, silica, or silicate. In one embodiment of the repair
composition, the first population of yttria-stabilized zirconia
particles, the second population of yttria-stabilized zirconia
particles, the third population of yttria-stabilized zirconia
particles, and the fourth population of yttria-stabilized zirconia
particles have from about 4 to about 60 mole percent yttrium oxide
content. In another embodiment, the first, the second, the third,
and the fourth populations of yttria-stabilized zirconia particles
have from about 4 to about 20 mole percent yttrium oxide content.
In another embodiment, the first, the second, the third, and the
fourth populations of yttria-stabilized zirconia particles have 8
mole percent yttrium oxide content.
[0041] In one embodiment, the aqueous binder includes water and a
binder selected from the group which includes water and
poly(alkylene carbonate) copolymer, cellulose binder, poly(vinyl
alcohol), and polyethylene glycol. For example, poly(propylene
carbonate), a binder for ceramic powders, is commercially available
under a trade name of QPAC.RTM. 40. In one embodiment, the aqueous
dispersant includes ammonium polyacrylate and water. Examples of
commercially available ammonium polyacrylate dispersing agents for
ceramic bodies are DARVAN.RTM. 821-A, DARVAN.RTM. 825, and Darvan
C.
[0042] In one embodiment, the aqueous ammonia solution includes
ammonia and water, wherein the ammonia is in an amount of from
about 25 to about 50 percent by volume of the aqueous ammonia
solution. In another embodiment, the aqueous ammonia solution
includes ammonia and water, wherein the ammonia is in an amount of
from about 40 to about 50 percent by volume of the aqueous ammonia
solution. In one embodiment the ammonia is in an amount of about 30
percent by volume of the aqueous ammonia solution.
[0043] The aqueous ammonia solution serves several roles in the
repair composition. The aqueous ammonia solution is a rheology
modifier, it is responsible for the thixotropic nature of the
repair composition. The aqueous ammonia solution also increases the
pH to the 9-11 range keeping the repair composition stable. We also
believe that the aqueous ammonia solution acts as a gelling agent
thereby increasing the green strength of the repaired area at room
temperature. The aqueous ammonia solution evaporates after the
repairing is completed. Upon evaporation the rheology increases and
sets the repair composition just like an epoxy.
[0044] One or more embodiments are directed to a method for
repairing a thermal barrier coating, wherein the thermal barrier
coating is located on a component and wherein the thermal barrier
coating has a damaged region, the method including: depositing a
repair layer onto the damaged region, the repair layer including
the described herein repair composition; and heat treating the
repair layer at a temperature of from about 900.degree. C. to about
1400.degree. C., to thereby form a patch. The damaged region may
be, for example, spallation, a chip, or a large damaged area. The
large damaged areas may be as large as 3 inches by 3 inches. In one
embodiment, the heat-treating temperature may be from about
1000.degree. C. to about 1200.degree. C. The heat-treating step, or
sintering, removes moisture and organic content from the repair
composition and it also forms a ceramic body with the desired
insulating properties. The heat treating may be localized to the
repair layer or entire part may be heat treated. Localized heat
treating may be performed with a torch, by induction, resistive
heating or other methods known in the art. When the entire part is
heat treated, the repair can be made while the engine is assembled
by simply running the engine to perform the heat-treating step. In
one embodiment, the repair layer includes only the repair
composition. FIG. 1 provides an idealized cross-sectional view of
the thermal barrier coating 10, the component 11, and the damaged
region 12. FIG. 2 provides an idealized cross-sectional view of the
thermal barrier coating 10, the component 11, and the repair layer
13.
[0045] In one embodiment, the method for repairing a thermal
barrier coating further includes, subsequent to the depositing of
the repair layer and prior to heat treating the repair layer,
drying the repair layer at a temperature of from about 50.degree.
C. to about 120.degree. C. In one embodiment, the drying
temperature may be from about 100.degree. C. to about 110.degree.
C. In another embodiment, the method for repairing a thermal
barrier coating further includes drying of the repair layer during
a warm up to the heat-treating temperature.
[0046] In one embodiment, the depositing of the repair layer onto
the damaged region is performed manually. In another embodiment,
the depositing of the repair layer onto the damaged region is
performed with an apparatus designed for such purpose.
[0047] In one embodiment, the thermal barrier coating is formed by
a plasma spray process. In another embodiment, the thermal barrier
coating is formed by an electron beam physical vapor deposition
process.
[0048] In one embodiment, the thermal barrier coating has a
thickness, i.e., depth, of from about 5 mils to about 25 mils. In
one embodiment, the repair layer has a thickness of from about 5
mils to about 25 mils. In one embodiment, the repair layer has
substantially the same thickness as a thickness of the thermal
barrier coating. The term "substantially the same thickness" as
used herein refers to thickness measurements that are equal or
within the range of about .+-.0.5 mils of each other.
[0049] In one embodiment, the component is disposed within a gas
turbine engine.
[0050] In one embodiment of the method for repairing a thermal
barrier coating, yttrium oxide content of the first, the second,
the third, and the fourth populations of yttria-stabilized zirconia
particles is the same as yttrium oxide content of the thermal
barrier coating being repaired.
[0051] In one embodiment of the method for repairing a thermal
barrier coating, the thermal barrier coating has a yttrium oxide
content of from about 4 mole percent to about 10 mole percent,
wherein the first population of yttria-stabilized zirconia
particles, the second population of yttria-stabilized zirconia
particles, the third population of yttria-stabilized zirconia
particles, and the fourth population of yttria-stabilized zirconia
particles have a yttrium oxide content that falls in a range of
about .+-.1 mole percent of the yttrium oxide content of the
thermal barrier coating.
[0052] In another embodiment of the method for repairing a thermal
barrier coating, the thermal barrier coating has a yttrium oxide
content of from about 10 mole percent to about 20 mole percent,
wherein the first population of yttria-stabilized zirconia
particles, the second population of yttria-stabilized zirconia
particles, the third population of yttria-stabilized zirconia
particles, and the fourth population of yttria-stabilized zirconia
particles have a yttrium oxide content that falls in a range of
about .+-.2 mole percent of the yttrium oxide content of the
thermal barrier coating.
[0053] In another embodiment of the method for repairing a thermal
barrier coating, the thermal barrier coating has a yttrium oxide
content of from about 20 mole percent to about 60 mole percent,
wherein the first population of yttria-stabilized zirconia
particles, the second population of yttria-stabilized zirconia
particles, the third population of yttria-stabilized zirconia
particles, and the fourth population of yttria-stabilized zirconia
particles have a yttrium oxide content that falls in a range of
about .+-.5 mole percent of the yttrium oxide content of the
thermal barrier coating.
[0054] In another embodiment, a method for repairing a thermal
barrier coating is provided. The thermal barrier coating is located
on a component and wherein the thermal barrier coating has a
damaged region, the method including: depositing an initial layer
onto the damaged area, the initial layer including the described
herein repair composition; heat treating the initial layer at a
temperature of from about 250.degree. C. to about 600.degree. C.;
optionally, repeating one or more times a combination of the steps
of depositing the initial layer onto the damaged area and heat
treating the initial layer at a temperature of from about
250.degree. C. to about 600.degree. C., to thereby form a plurality
of initial layers; depositing a final layer onto the initial layer
or onto the plurality of initial layers, the final layer comprising
the repair composition; and concurrently heat treating the final
layer and the initial layer at a temperature of from about
900.degree. C. to about 1400.degree. C., to thereby form a patch,
or concurrently heat treating the final layer and the plurality of
initial layers at a temperature of from about 900.degree. C. to
about 1400.degree. C., to thereby form the patch. The heat-treating
steps may be performed as described above. In one embodiment, the
repair layer and the final layer include only the repair
composition. FIG. 3 provides an idealized cross-sectional view of
the thermal barrier coating 10, the component 11, the initial layer
14, and the final layer 15.
[0055] In one embodiment, the heat treating of the initial layer
temperature may be from about 300.degree. C. to about 500.degree.
C. In one embodiment, the temperature of concurrently heat treating
the final layer and the initial layer may be from about
1000.degree. C. to about 1200.degree. C. In one embodiment, the
temperature of concurrently heat treating the final layer and the
plurality of initial layers may be from about 1000.degree. C. to
about 1200.degree. C.
[0056] In one embodiment, the method further includes, subsequent
to the depositing of the initial layer and prior to heat treating
the initial layer, drying the initial layer at a temperature of
from about 50.degree. C. to about 120.degree. C. In one embodiment,
the drying temperature may be from about 100.degree. C. to about
110.degree. C. In one embodiment, the method further includes
drying of the initial layer during a warm up to the temperature of
the heat treating of the initial layer.
[0057] In one embodiment, the method further includes, subsequent
to deposition the final layer and prior to concurrently heat
treating the final layer and the initial layer, drying the final
layer at a temperature of from about 50.degree. C. to about
120.degree. C., or subsequent to deposition of the final layer and
prior to concurrently heat treating the final layer and the
plurality of initial layers, drying the final layer at a
temperature of from about 50.degree. C. to about 120.degree. C. In
one embodiment, the drying temperature may be from about
100.degree. C. to about 110.degree. C.
[0058] In one embodiment, the method further includes, subsequent
to deposition the final layer and prior to concurrently heat
treating the final layer and the initial layer, drying the final
layer during a warm up to the temperature of the concurrent heat
treating of the final layer and initial layer, or subsequent to
deposition the final layer and prior to concurrently heat treating
the final layer and the plurality of initial layers, drying the
final layer during a warm up to the temperature of the concurrent
heat treating of the final layer and the plurality of initial
layers.
[0059] In one embodiment, the thermal barrier coating is formed by
a plasma spray process. In another embodiment, the thermal barrier
coating is formed by an electron beam physical vapor deposition
process.
[0060] In one embodiment, the depositing of the initial layer and
the final layer is performed manually.
[0061] In one embodiment, the thermal barrier coating has a
thickness of from about 5 mils to about 95 mils. In one embodiment,
the initial layer has a thickness of from about 5 mils to about 25
mils. In one embodiment, the final layer has a thickness of from
about 5 mils to about 25 mils. In one embodiment, the plurality of
initial layers comprises from 2 to 4 initial layers. In one
embodiment, a combination of the initial layer and the final layer
has substantially the same thickness as a thickness of the thermal
barrier coating. In another embodiment, a combination of the
plurality of initial layers and the final layer has substantially
the same thickness as a thickness of the thermal barrier coating.
The term "substantially the same thickness" as used herein refers
to thickness measurements that are equal or within the range of
about .+-.0.5 mils of each other.
[0062] In one embodiment, the component is disposed within a gas
turbine engine.
[0063] In one embodiment, the first population of yttria-stabilized
zirconia particles, the second population of yttria-stabilized
zirconia particles, the third population of yttria-stabilized
zirconia particles, and the fourth population of yttria-stabilized
zirconia particles have from about 4 to about 60 mole percent
yttrium oxide content. In another embodiment, the first, the
second, the third, and the fourth populations of yttria-stabilized
zirconia particles have from about 4 to about 20 mole percent
yttrium oxide content.
[0064] In one embodiment of the method for repairing a thermal
barrier coating, yttrium oxide content of the first, the second,
the third, and the fourth populations of yttria-stabilized zirconia
particles is the same as yttrium oxide content of the thermal
barrier coating being repaired.
[0065] In one embodiment of the method for repairing a thermal
barrier coating, the thermal barrier coating has a yttrium oxide
content of from about 4 mole percent to about 10 mole percent,
wherein the first population of yttria-stabilized zirconia
particles, the second population of yttria-stabilized zirconia
particles, the third population of yttria-stabilized zirconia
particles, and the fourth population of yttria-stabilized zirconia
particles have a yttrium oxide content that falls in a range of
about .+-.1 mole percent of the yttrium oxide content of the
thermal barrier coating.
[0066] In another embodiment of the method for repairing a thermal
barrier coating, the thermal barrier coating has a yttrium oxide
content of from about 10 mole percent to about 20 mole percent,
wherein the first population of yttria-stabilized zirconia
particles, the second population of yttria-stabilized zirconia
particles, the third population of yttria-stabilized zirconia
particles, and the fourth population of yttria-stabilized zirconia
particles have a yttrium oxide content that falls in a range of
about .+-.2 mole percent of the yttrium oxide content of the
thermal barrier coating.
[0067] In another embodiment of the method for repairing a thermal
barrier coating, the thermal barrier coating has a yttrium oxide
content of from about 20 mole percent to about 60 mole percent,
wherein the first population of yttria-stabilized zirconia
particles, the second population of yttria-stabilized zirconia
particles, the third population of yttria-stabilized zirconia
particles, and the fourth population of yttria-stabilized zirconia
particles have a yttrium oxide content that falls in a range of
about .+-.5 mole percent of the yttrium oxide content of the
thermal barrier coating.
[0068] This written description uses examples to disclose
embodiments of the inventive subject matter, including the best
mode, and also to enable any person skilled in the art to practice
the inventive subject matter, including making and using any
devices or systems and performing any incorporated methods. The
patentable scope of the inventive subject matter is not limited to
the scope of the provided examples, and may include other examples
that occur to those skilled in the art. Such other examples are
intended to be within the scope of the claims if they have
structural elements or method steps that do not differ from the
literal language of the claims, or if they include equivalent
structural elements or method steps with insubstantial differences
from the literal language of the claims.
EXAMPLES
Example 1
Repair Composition
[0069] The following Table 1 represents one example of a repair
composition according to an embodiment.
TABLE-US-00001 TABLE 1 Repair composition example. Material Vol %
Fine particles of the ceramic composition (first 15 population of
yttria-stabilized zirconia particles, d50 = 800 nm .+-. 100 nm, 4
mol % YSZ) Medium particles of the ceramic composition 10 (second
population of yttria-stabilized zirconia particles, d50 = 4 .mu.m
.+-. 1 .mu.m, 4 mol % YSZ) Large particles of the ceramic
composition 30 (third population of yttria-stabilized zirconia
particles, d50 = 25 .mu.m .+-. 3 .mu.m, 4 mol % YSZ) NYACOL .RTM.
ZRYS4 (colloidal solution with 20 fourth population of
yttria-stabilized zirconia particle, d50 = 100 nm .+-. 50 nm, 1.32
wt % YSZ) QPAC .RTM. 40 Poly(propylene carbonate) 10 (aqueous
binder) DARVAN .RTM. 825 (aqueous dispersant) 6 Aqueous ammonia
(30% volume 9 concentration of ammonia)
Example 2
Preparation of Repair Composition
[0070] To prepare the repair composition of Example 1, first, three
different powders (Fine particles, (18.5 gm) Medium particles, (12
gm) and Large particles (41 gm)) were weighed, put in a NALGENE.TM.
bell mouth bottle, and mixed using THINKY.RTM. planetary mixer at
1500 rpm for 3 min. This step was followed by a visual inspection
to ensure homogenous distribution of large, medium and fine
particles in the dry powder. The container was then opened, and
visually inspected by rolling around to ensure uniform colorization
of powders, indicating that the mix is well distributed. Next, 3 ml
of QPAC.RTM. 40 (aqueous binder), 1.5 ml of DARVAN.RTM. 825
(aqueous dispersant), 5 ml of NYACOL.RTM. ZRYS4 (colloidal solution
with fourth population of yttria-stabilized zirconia particles,
d50=100 nm), and 2 ml of ammonia aqueous solution of 30% vol
ammonia were added to the powders and mixed using THINKY.RTM.
planetary mixer at 1500 rpm for 3 min. Mixing step was repeated in
order to ensure slurry homogeneity without any agglomerates.
Example 3
Method of Repairing a Thermal Barrier Coating (TBC)
[0071] A piece measuring 4.times.4 inches was cut from a field
returned combustor liner. The field returned combustor liner had 4
mole percent yttrium oxide content. From this section, 1-inch
diameter round 6 samples were cut. A simulated 0.75-inch circular
defect was created on each sample by grit blasting for 6-10 seconds
with abrasive 60 grit alumina particles at 60 psi with standoff
distance of 4 inches to simulate damage from operation of a
turbine. The grit blasted field returned liner was cleaned first
with acetone and later in isopropanol using ultrasonic bath for 20
minutes. The damaged region was cleaned in order to remove any TBC
debris. After cleaning, the damaged TBC part was dried at room
temperature and then the repair composition of Example 1 was
deposited on the damaged region using a steel spatula, thus forming
a repair layer. The top surface of the repair layer was leveled
with the remnant TBC using doctor blade. Subsequently, the repair
layer was first dried at room temperature for 2 hours and then at
100.degree. C. for 4 hours. The repair layer was then sintered at
1000.degree. C. for 6 hour in air, thereby forming a patch on the
TBC part.
[0072] As discussed below, the repaired samples from Example 3 were
tested in two different modes to simulate the thermal conditions in
an engine. The first is called furnace cycle test (FCT) and the
second is called the jet engine thermal shock (JETS) test. FCT
tests were conducted isothermally in a bottom-loaded rapid heating
furnace. JETS tests were conducted using a natural gas/oxygen
mixture gas torch where the heat input was controlled to obtain a
thermal gradient across the sample thickness. As discussed below,
samples from Example 3 were also tested for adhesion using an ASTM
standard to understand how the repaired coating has adhered to the
bond coat.
Example 4
Furnace Cycle Testing (FCT)
[0073] 50 specimens were subjected to cyclic thermal exposure in a
furnace cycle test (FCT) after repairing samples as described in
Example 3 using the repair composition described in Example 1.
During a 1 hour cycle, the specimens were inserted rapidly into a
bottom-loading furnace and held at 1135.degree. C. for 45 min. The
specimens were then withdrawn from the furnace and forced-air
cooled for 15 min before beginning the next cycle. Specimens were
removed from the FCT and examined after 20 cycles. The samples
remained in the test until spallation of 20% of the coating area to
determine the FCT life. Out of 50 samples tested, the median life
was 220 cycles.
Example 5
Tensile Pull Adhesion Testing
[0074] After repairing samples as described in Example 3 using the
repair composition described in Example 1, tensile adhesion
strength was measured on 20 repaired samples following the Standard
Test Method for Adhesion or Cohesion Strength of Flame-Sprayed
Coatings as per ASTM standard C633-79. Right circular cylindrical
fixtures (2.54 cm height and 1.91 cm diameter) were attached to the
surfaces of the TBC and the substrate using an adhesive Cytec
FM1000. A tensile load was applied at a constant displacement rate
of 0.017 mm/s until the coating delaminated from the substrate. The
tensile adhesion strength was determined from the area and the
maximum load at failure. Out of 20 samples tested, the median
adhesion strength was 1185 psi.
Example 6
Jet Engine Thermal Shock (JETS) Testing
[0075] After repairing samples as described in Example 3 using the
repair composition described in Example 1, JETS tests were
performed. The JETS test creates a thermal gradient equivalent to a
jet engine across the TBC. TBC front surface temperature was
1235.degree. C. (2250 F). An oxygen-natural gas torch heated a
2.54-inch diameter in 8 repaired samples, which were attached to a
carousel. A stepping motor advanced the buttons (i.e., repaired
samples) through the positions. Under our testing protocol, the
repaired samples remained in the test either until 2000 cycles were
completed or until spallation of 20% of the coated area. All eight
samples were tested at these conditions. All of the tested repaired
samples withstood 2000 cycles and none of the tested repaired
samples spalled.
[0076] While only certain features of the inventive subject matter
have been illustrated and described herein, many modifications and
changes will occur to those skilled in the art. It is, therefore,
to be understood that the appended claims are intended to cover all
such modifications and changes as falling within the true spirit of
the inventive subject matter.
[0077] Throughout this application, various references are referred
to. The disclosures of these publications in their entireties are
hereby incorporated by reference as if written herein.
* * * * *