U.S. patent application number 12/638051 was filed with the patent office on 2011-06-16 for plasma application of thermal barrier coatings with reduced thermal conductivity on combustor hardware.
This patent application is currently assigned to UNITED TECHNOLOGIES CORPORATION. Invention is credited to Susan M. Meier, Kevin W. Schlichting, Paul H. Zajchowski.
Application Number | 20110143043 12/638051 |
Document ID | / |
Family ID | 43218439 |
Filed Date | 2011-06-16 |
United States Patent
Application |
20110143043 |
Kind Code |
A1 |
Zajchowski; Paul H. ; et
al. |
June 16, 2011 |
PLASMA APPLICATION OF THERMAL BARRIER COATINGS WITH REDUCED THERMAL
CONDUCTIVITY ON COMBUSTOR HARDWARE
Abstract
A process for forming a thermal barrier coating comprises the
steps of providing a substrate, providing a gadolinia stabilized
zirconia powder, and forming a thermal barrier coating having at
least one of a porosity in a range of from 5 to 20% and a dense
segmented structure on said substrate by supplying the gadolinia
stabilized powder to a spray gun and using an air plasma spray
technique.
Inventors: |
Zajchowski; Paul H.;
(Enfield, CT) ; Meier; Susan M.; (Vernon, CT)
; Schlichting; Kevin W.; (South Glastonbury, CT) |
Assignee: |
UNITED TECHNOLOGIES
CORPORATION
Hartford
CT
|
Family ID: |
43218439 |
Appl. No.: |
12/638051 |
Filed: |
December 15, 2009 |
Current U.S.
Class: |
427/455 |
Current CPC
Class: |
C23C 4/11 20160101; C23C
4/134 20160101 |
Class at
Publication: |
427/455 |
International
Class: |
C23C 4/08 20060101
C23C004/08 |
Goverment Interests
STATEMENT OF GOVERNMENT INTEREST
[0001] The Government of the United States of America may have
rights in the present invention as a result of Contract No.
N00019-02-C-3003 awarded by the Department of the Air Force.
Claims
1. A process for forming a thermal barrier coating comprising the
steps of: providing a substrate; providing a gadolinia stabilized
zirconia powder; and forming a thermal barrier coating having at
least one of a porosity in a range of from 5 to 20% and a dense
segmented structure on said substrate by supplying the gadolinia
stabilized powder to a spray gun and using an air plasma spray
technique.
2. The process according to claim 1, wherein said substrate
providing step comprises providing a combustor component.
3. The process according to claim 1, wherein said substrate
providing step comprises providing one of a combustor panel, a
combustor chamber, a combustor heat shield, a combustor transition
duct, and a combustor augmentor.
4. The process according to claim 1, wherein said powder providing
step comprises providing a powder consisting of optionally from 3.0
to 14 wt % of at least one of yttria and titania, from 15 to 70 wt
% gadolinia, and the balance zirconia.
5. The process according to claim 1, wherein said powder providing
step comprises providing a powder consisting of from 3.0 to 14 wt %
of at least one of yttria and titanium, from 15 to 70 wt %
gadolinia, and the balance zirconia.
6. The process according to claim 1, wherein said thermal barrier
coating forming step comprises using an amperage range of 350 to
825 amps, a voltage of 35 to 50 volts, an argon primary gas flow of
75 to 105 SCFH, at least one of a hydrogen secondary gas flow of
1.0 to 10 SCFH and a helium secondary gas flow of 45 to 75 SCFH, a
powder gas flow exiting a spray gun of 4.0 to 20 SCFH, a powder
feed rate to the spray gun of 10 to 40 grams/min., and a gun
distance from a surface of the substrate being coated of from 3.0
to 5.0 inches.
7. The process according to claim 1, wherein said thermal barrier
coating forming step comprises using an amperage range of from 500
to 700 amps, a voltage of 55 to 65 volts, an argon primary gas flow
of 65 to 90 SCFH, a hydrogen secondary gas flow of 8 to 22 SCFH, a
powder gas flow from a spray gun of 6 to 12 SCFH, a powder feed
rate to the spray gun of 35 to 55 grams/min. and a gun distance
from a surface of a substrate being coated of from 4.0 to 7.0
inches.
8. The process according to claim 1, further comprising depositing
a ceramic interlayer on said substrate prior to said thermal
barrier coating step.
9. The process according to claim 8, wherein said ceramic
interlayer depositing step comprises depositing a layer of 7.0 wt %
yttria stabilized zirconia.
10. The process according to claim 8, further comprising depositing
a bondcoat layer on said substrate prior to said ceramic interlayer
depositing step.
11. The process according to claim 10, wherein said bondcoat layer
depositing step comprises depositing a metallic bondcoat layer.
12. The process according to claim 1, wherein said thermal barrier
coating forming step comprises forming a segmented coating having a
thermal conductivity in the range of from 5.0 to 12.5 BTU in/hr
ft.sup.2 F.
13. The process according to claim 1, wherein said thermal barrier
coating forming step comprises forming a porous coating having a
thermal conductivity in the range of from 3.0 to 10 BTU in/hr
ft.sup.2 F.
Description
BACKGROUND
[0002] The present disclosure is directed to thermal barrier
coatings with reduced thermal conductivity on combustor hardware,
which coatings are applied using a plasma.
[0003] Ceramic thermal barrier coatings (TBCs) have been used for
many years to extend the life of combustors and high turbine
stationary and rotating parts in gas turbine engines. TBCs
typically consist of a metallic bond coat and a ceramic top coat
applied to a nickel or cobalt based alloy substrate which forms the
part being coated. The coatings are typically applied to
thicknesses between 5 and 40 mils and can provide up to 300 degrees
F. temperature reduction to the substrate metal. This temperature
reduction translates into improved part durability, higher turbine
operating temperatures, and improved turbine efficiency. Typically,
the ceramic layer is a 7 wt % yttria stabilized zirconia applied by
air plasma spray (APS). New low thermal conductivity coatings have
been developed which can provide improved part performance.
[0004] One coating which has been used in the past for TBCs is
gadolinia stabilized zirconia based thermal barrier coatings.
SUMMARY OF THE INVENTION
[0005] It is desirable to form a thermal barrier coating which has
a relatively low thermal conductivity.
[0006] As described herein, there is provided a process for forming
a thermal barrier coating comprises the steps of providing a
substrate, providing a gadolinia stabilized zirconia powder, and
forming a thermal barrier coating having at least one of a porosity
in a range of from 5 to 20% and a dense segmented structure on said
substrate by supplying the gadolinia stabilized powder to a spray
gun and using an air plasma spray technique.
[0007] Other details of the thermal barrier coatings applied using
an air plasma spray technique, as well as advantages attendant
thereto, are set forth in the following detailed description and
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIGS. 1 and 2 are photomicrographs showing a low
conductivity cracked coating formed using a F4 Plasma Spray Gun,
which coating includes a ceramic layer consisting of 30 wt %
Gd.sub.2O.sub.3 and 70 wt % ZrO.sub.2 with a air plasma sprayed
MCrAlY bond coat);
[0009] FIG. 3 is a photomicrograph showing a coating system which
includes a metallic bond coat, a ceramic bond coat, and a ceramic
top coat formed by a low conductivity coating in which the metallic
bond coat is an air plasma-sprayed MCrAlY bond coat, the ceramic
bond coat is a 7 YSZ interlayer, and the ceramic top coat is a 30
wt % Gd.sub.2O.sub.3--70 wt % ZrO.sub.2 top layer.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0010] As described herein, a plasma spray technique is utilized to
apply a gadolinia stabilized zirconia based thermal barrier
coatings on combustor hardware such as panels, chambers, heat
shields, transition ducts, augmenters, etc. The plasma spray
technique may be an air plasma spray technique in which a desirable
coating microstructure is produced.
[0011] In air plasma spray, the coating material is propelled
toward the surface of the substrate to be coated. The coating
material is in the form of a spray. The powder or powders forming
the coating material are fed along with carrier gases into a high
temperature plasma gas stream. In the plasma gas stream, the powder
particles are melted and accelerated toward the surface of the
substrate to be coated. The powder particles are fed to a spray gun
at a desired feed rate. A carrier gas flow such as an argon gas
flow is used to maintain the powder under pressure and facilitate
powder feed. The carrier gas flow rate is described in standard
cubic feet per hour. Standard conditions may be defined as about
room temperature and about one atmosphere of pressure.
[0012] The gases that make up the plasma gas stream comprise a
primary gas (such as an argon gas or nitrogen gas) and a secondary
gas (such as a hydrogen gas). Helium gas may be used as the
secondary gas if desired.
[0013] The process includes the step of translating a spray gun so
that the nozzle is positioned at a desired distance from the
surface to be coated. The substrate to be coated may be passed
through the spray of powder particles emanating from the spray
gun.
[0014] The spray gun to be used to form the coatings disclosed
herein may include both internal feed and external feed spray guns.
Suitable spray guns include the Plasmadyne SG-100, Sulzer Metco 3
MB, 7 MB, or 9 MB, and the Plasma Technic F-4. The desired coating
may also be applied with the high deposition rate Sulzer Metco
Triplex gun and/or the Progressive HE100 gun.
[0015] Zirconia based powder with the additions of rare earth
stabilizers, such as gadolinia, have been found to yield coatings
having lower thermal conductivities than many current thermal
barrier coatings. A useful zirconia based powder is one which
consists of optionally 3.0 to 14 wt % of at least one of yttria and
titania, 15 to 70 wt % gadolinia, and the balance zirconia. The
yttria and/or titania, and the gadolinia, improve the thermal
barrier coating's ceramic mechanical properties, while still
achieving a reduced thermal conductivity ceramic coating. Coatings
formed using these powders are shown in FIGS. 1 and 2.
[0016] If desired, one could apply to a substrate, a coating which
has a metallic bond coat, such as a MCrAlY type coating where M is
Ni or Co, a ceramic interlayer, such as a 7 YSZ coating, deposited
on the metallic bond coat and a ceramic top coat comprising from 15
to 70 wt % gadolinia and the balance zirconia. Such a coating
system is illustrated in FIG. 3.
[0017] The air plasma spray parameters may be adjusted to produce a
coating with a desired level of porosity or a coating with a dense
segmented structure. For porous coatings, the coating may have a
thermal conductivity which ranges from 3.0 to 10 BTU in/hr ft.sup.2
F. For segmented coatings, the coating may have a thermal
conductivity which ranges from 5.0 to 12.5 BTU in/hr ft.sup.2
F.
[0018] A useful coating has a porosity in the range of 5.0 to 20%.
The desired porosity for the coating may be obtained by altering
the gun power settings, the standoff distance, the powder particle
size, and the powder feed rate.
[0019] Segmented coatings provide the coating with strain tolerance
during operation which leads to increased spallation life. For
combustor panel applications, a coating system having a segmented
microstructure topcoat layer with a ceramic interlayer provides a
useful coating system.
[0020] If desired, one can obtain a coating with a dense segmented
structure by increasing the power settings and shorten the standoff
distance. One can do this by using the settings set forth in
columns 6-8 of U.S. Pat. No. 5,879,753, which patent is
incorporated by reference herein.
[0021] For example, a useful coating may be applied using the
Plasmadyne SG-100 spray gun using an amperage range of 350 to 825
amps, a voltage of 35 to 50 volts applied to a cathode and anode
within the plasma-gun body, an argon primary gas flow of 75-105
SCFH, a hydrogen secondary gas flow of 1.0 to 10 SCFH or a helium
gas flow of 45-75 SCFH, a powder gas flow exiting the gun of 4.0 to
20 SCFH, a powder feed rate to the gun of 10 to 40 grams/min., and
a gun distance from the surface being coated of from 3.0 to 5.0
inches. Alternatively, the coatings may be applied with the Plasma
Technic F-4 spray gun using an amperage range of from 500 to 700
amps, a voltage of 55 to 65 volts, an argon primary gas flow of 65
to 90 SCFH, a hydrogen secondary gas flow of 8-22 SCFH, a powder
gas flow from the spray gun of 6 to 12 SCFH, a powder feed rate to
the spray gun of 35-55 grams/min. and a gun distance from the
surface being coated of from 4.0 to 7.0 inches.
[0022] One of the benefits of the process of the present invention
is the application of a thermal barrier coating having lower
thermal conductivity than many current coatings resulting in longer
coating life, performance improvements, and cost savings.
[0023] Burner rig testing of a low conductivity coating formed in
accordance with the present disclosure with a ceramic interlayer
was found to be 1.6 to 1.9 times better in spallation resistance
than without the interlayer. In addition, low conductivity coatings
with an interlayer are 1.3 to 1.5 times better in spallation than
current coatings.
[0024] In accordance with the foregoing disclosure, there has been
provided a plasma application of thermal barrier coatings with
reduced thermal conductivity on combustor hardware. While the
plasma application of thermal barrier coatings has been described
in the context of specific embodiments thereof, other unforeseeable
alternatives, modifications, and variations may become apparent to
those skilled in the art having read the foregoing description.
Accordingly, it is intended to embrace those alternatives,
modifications, and variations as fall within the broad scope of the
appended claims.
* * * * *