U.S. patent application number 13/716278 was filed with the patent office on 2014-06-19 for erosion and corrosion resistant components and methods thereof.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. The applicant listed for this patent is GENERAL ELECTRIC COMPANY. Invention is credited to Jane Marie Lipkin, Vinod Kumar Pareek.
Application Number | 20140166473 13/716278 |
Document ID | / |
Family ID | 50929675 |
Filed Date | 2014-06-19 |
United States Patent
Application |
20140166473 |
Kind Code |
A1 |
Lipkin; Jane Marie ; et
al. |
June 19, 2014 |
EROSION AND CORROSION RESISTANT COMPONENTS AND METHODS THEREOF
Abstract
A coating system and a method of applying the coating system on
an article. The coating system includes a sacrificial coating on a
surface of the article and an erosion-resistant coating on the
sacrificial coating, wherein the erosion-resistant coating
comprises a layer of a polymeric material. The sacrificial coating
is more anodic than the surface or the erosion-resistant
coating.
Inventors: |
Lipkin; Jane Marie;
(Niskayuna, NY) ; Pareek; Vinod Kumar; (Albany,
NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GENERAL ELECTRIC COMPANY |
Schenectady |
NY |
US |
|
|
Assignee: |
GENERAL ELECTRIC COMPANY
Schenectady
NY
|
Family ID: |
50929675 |
Appl. No.: |
13/716278 |
Filed: |
December 17, 2012 |
Current U.S.
Class: |
204/196.1 ;
427/58 |
Current CPC
Class: |
F05D 2300/43 20130101;
F05D 2300/603 20130101; F04D 29/324 20130101; C23F 13/14 20130101;
F04D 29/023 20130101; F05D 2300/501 20130101; F01D 5/288
20130101 |
Class at
Publication: |
204/196.1 ;
427/58 |
International
Class: |
C23F 13/18 20060101
C23F013/18; C23F 13/14 20060101 C23F013/14 |
Claims
1. A coating system for an article, the coating system comprising:
a sacrificial coating deposited on a surface of the article; and an
erosion-resistant coating deposited on the sacrificial coating
comprising a layer of a polymeric material, wherein the sacrificial
coating is more anodic than both the surface and the
erosion-resistant coating.
2. The coating system of claim 1, wherein the article comprises a
stainless steel or a superalloy.
3. The coating system of claim 1, wherein the sacrificial coating
comprises a layer of Al, Cr, Zn, an Ni--Al alloy, an Al--Si alloy,
an Al-based alloy, a Cr-based alloy or a Zn-based alloy, an Al
polymer composite, or a combination thereof.
4. The coating system of claim 1, wherein the sacrificial coating
comprises a layer of a conductive undercoat and a layer of an
overcoat disposed on the undercoat, the overcoat comprising an
inorganic matrix binder having a plurality of ceramic particles and
conductive particles embedded therein.
5. The coating system of claim 1, wherein the polymeric material of
the erosion-resistant coating comprises siloxanes, silicon alkyds,
and flurosilicones, modified bituminous materials, modified tar,
epoxy-based materials, elastomers, polybutadiene, neoprene, butyl
rubber, or a combination thereof.
6. The coating system of claim 1, further comprising a primer
material layer between the sacrificial coating and the
erosion-resistant coating.
7. The coating system of claim 1, wherein the article is a
compressor blade of a gas turbine.
8. The coating system of claim 1, wherein the sacrificial coating
has a thickness of about 5 to about 50 micrometers.
9. The coating system of claim 1, wherein the erosion-resistant
coating has a thickness of about 50 to about 125 micrometers.
10. The article comprising the coating system of claim 1
thereon.
11. A method of applying a coating system on an article, the method
comprising: depositing a sacrificial coating on a surface of the
article; and then depositing an erosion-resistant coating on the
sacrificial coating, the erosion-resistant coating comprising a
layer of a polymeric material, wherein the sacrificial coating is
more anodic than the surface of the article or the
erosion-resistant coating.
12. The method of claim 11, wherein depositing the sacrificial
coating produces a residual compressive stress in the sacrificial
coating.
13. The method of claim 11, wherein the surface of the article is
defined by a substrate formed of a stainless steel or a
superalloy.
14. The method of claim 11, wherein the sacrificial coating
comprises a layer of Al, Cr, Zn, an Ni--Al alloy, an Al--Si alloy,
an Al-based alloy, a Cr-based alloy or a Zn-based alloy, an Al
polymer composite, or a combination thereof.
15. The method of claim 11, wherein the sacrificial coating
comprises a layer of a conductive undercoat and a layer of an
overcoat disposed on the undercoat, the overcoat comprising an
inorganic matrix binder having a plurality of ceramic particles and
conductive particles embedded therein.
16. The method of claim 11, wherein the polymeric material of the
erosion-resistant coating comprises siloxanes, silicon alkyds, and
flurosilicones, modified bituminous materials, modified tar,
epoxy-based materials, elastomers, polybutadiene, neoprene, butyl
rubber, or a combination thereof.
17. The method of claim 11, further comprising depositing a primer
material layer between the sacrificial coating and the
erosion-resistant coating prior to depositing the erosion-resistant
coating.
18. The method of claim 11, wherein the article is a compressor
blade of a gas turbine.
19. The method of claim 11, wherein the sacrificial coating has a
thickness of about 5 to about 50 micrometers.
20. The method of claim 11, wherein the erosion-resistant coating
has a thickness of about 50 to about 125 micrometers.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention generally relates to coatings capable
of exhibiting erosion and/or corrosion resistance. More
particularly, this invention relates to coatings suitable for use
on airfoil components, including compressor airfoils of gas
turbines, to promote the corrosion and erosion resistance thereof
and to methods of manufacturing airfoil components with such
coatings.
[0002] Stainless steel blades, such as those used in the
compressors of land-based gas turbine engines used in industrial
applications (for example, power generation), have shown
susceptibility to erosion and corrosion pitting of their airfoil
surfaces that are believed to be associated with various
electrochemical dissolution processes enabled by the impingement of
water droplets and chemical species present in the droplets, intake
air, and combinations thereof. Electrochemically-induced corrosion
and erosion phenomena occurring at the airfoil surfaces can in turn
result in cracking of the components due to the cyclic thermal and
operating stresses experienced by these components. Water droplet
exposure can result from use of on-line water washing, fogging and
evaporative cooling, or various combinations of these processes
that may be employed to enhance compressor efficiency. Water
droplet exposure can also result from the environments in which
land-based gas turbines operate, for example, highly corrosive
environments such as those near chemical or petrochemical plants
where various chemical species may be found in the intake air, or
those at or near ocean coastlines or other saltwater environments
where various sea salts may be present in the intake air, or
combinations of the above, or in other applications where the inlet
air contains corrosive chemical species.
[0003] Though improvements in erosion and/or corrosion resistance
can be achieved through the use of different materials, such as
nickel-base or titanium-base alloys, this approach may not solve
water droplet erosion or corrosion pitting problems since these
materials may also have susceptibility to the associated
electrochemical processes. Other potential drawbacks to the use of
materials other than stainless steels include higher costs of their
alloy constituents, the need for redesign of the blades, including
airfoil surfaces, due to the different metallurgical and mechanical
properties of the materials, and issues relating to overall
robustness of the blades resulting from potential sensitivity to
other degradation phenomena, such as various rub and fretting wear
mechanisms.
[0004] Corrosion-resistant airfoil coatings and methods of making
steel airfoil components with corrosion-resistant coatings are
described in U.S. Pat. Nos. 5,098,797 and 5,260,099 to Haskell.
These patents describe a corrosion-resistant coating that includes
a sacrificial undercoat of a metal that is above iron in the
electromotive series, and a ceramic overcoat. The ceramic material
is applied at a temperature of 600.degree. F. or less to avoid
reduction of fatigue resistance of the alloy used to form the
component, which is disclosed as a stainless steel alloy.
[0005] While approaches of the type disclosed in the Haskell
patents are capable of improving the erosion or corrosion
resistance of stainless steel compressor blades, additional
approaches for achieving further improvements would be
desirable.
BRIEF DESCRIPTION OF THE INVENTION
[0006] The present invention provides a method suitable for
depositing a coating system on an article, such as a compressor
blade of a land-based gas turbine, and a coating system deposited
thereby that provides improved corrosion and erosion resistance to
the article.
[0007] According to a first aspect of the invention, a coating
system for an article includes a sacrificial coating on a surface
of the article and an erosion-resistant coating on the sacrificial
coating. The erosion-resistant coating comprises a layer of a
polymeric material, and the sacrificial coating is more anodic than
both the surface and the erosion-resistant coating.
[0008] According to a second aspect of the invention, a method of
applying a coating system on an article includes depositing a
sacrificial coating on a surface of the article and depositing an
erosion-resistant coating on the sacrificial coating, wherein the
erosion-resistant coating comprises a layer of a polymeric
material. The sacrificial coating is more anodic than both the
surface of the article and the erosion-resistant coating.
[0009] A technical effect of the invention is the ability to
improve the corrosion and erosion resistance of articles that are
subjected to erosion and/or corrosion, including compressor blades
that are susceptible to water droplet erosion and corrosion
pitting. In particular, it is believed that, by providing such an
article with a sacrificial coating that is more anodic than the
surface of the article and providing an erosion-resistant coating
thereon formed of a polymeric material, the corrosion and erosion
resistance of the article can be significantly improved.
[0010] Other aspects and advantages of this invention will be
better appreciated from the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is schematic perspective view of a compressor blade
of a type used in gas turbine engines and suitable for protection
with coatings in accordance with an aspect of the invention.
[0012] FIG. 2 is a cross-sectional view of section 2-2 of FIG.
1.
[0013] FIG. 3 is a schematic cross-sectional view of an embodiment
of region 90 of FIG. 2.
DETAILED DESCRIPTION OF THE INVENTION
[0014] The present invention will be described below in reference
to airfoil components whose airfoil surfaces are protected by a
coating system that includes a sacrificial coating and an
erosion-resistant coating. The coating system is particularly
useful for use within the compressor sections of land-based gas
turbine engines, including components such as rotating compressor
blades and stationary compressor vanes, shrouds, and other surfaces
within the compressor section. The coating system may also be
applicable to other components that may be subject to water droplet
erosion and/or pitting and crevice corrosion, nonlimiting examples
of which include vanes, nozzles and shrouds within the turbine
section of a gas turbine engine, combustor liners, diaphragm
components, seal components, valve stems, nozzle boxes, nozzle
plates, and the like as well as components in steam turbines.
[0015] FIG. 1 schematically represents a compressor blade 1 of a
type that may be used in land-based gas turbine engines. The blade
1 comprises an airfoil 10 whose surfaces are desired to exhibit
improved resistance to particle impact, water droplet erosion and
crevice corrosion. The blade 1 is represented as configured to be
removably attached to a central hub or disk, though the blade 1
could alternatively be an integral portion of a hub or disk, in
which case the combination of the hub/disk and its blades is
commonly referred to as a blisk. However, while the embodiments
herein are illustrated with reference to the particular compressor
blade 1 represented in FIG. 1, they are broadly applicable to a
wide variety of other gas turbine engine components, as previously
noted.
[0016] Referring to FIG. 1, the blade 1 is illustrated as having,
in addition to the airfoil 10, a leading edge 14, a trailing edge
18, a tip edge 22 and a blade root 26. The span 28 of the airfoil
10 extends from the tip edge 22 to the blade root 26. The surface
of the airfoil 10 comprehended within the span 28 constitutes an
airfoil surface 32 of the blade 1, and is therefore exposed to the
flow path of air entering the gas turbine engine at its inlet (not
shown) upstream of the compressor section.
[0017] FIG. 2 shows the airfoil surface 32 of the airfoil 10 as
comprising convex and concave surfaces 30 and 34 that extend
between the leading edge 14 and trailing edge 18. The dashed line
38 extending from the leading edge 14 to the trailing edge 18
defines the width or chord of the airfoil 10. The double-headed
arrow 42 between the convex and concave surfaces 30 and 34 defines
the thickness (usually measured as the "maximum" thickness) of the
airfoil 10.
[0018] The greatest erosion and corrosion damage to the airfoil
surface 32 tends to occur at a leading edge section 46 of the
airfoil 10, particularly with regard to the initiation of erosion
or corrosion pitting, and especially at or proximate to the leading
edge 14. Referring to FIGS. 1 and 2, the area of greatest erosion
damage tends to occur in a tip edge portion 50 of the airfoil 10
that defines the tip edge 22, and especially at or proximate to the
tip edge 22, and also tends to be focused in a portion 54 of the
concave surface 34 represented in FIG. 2 as directly forward of the
trailing edge 18 and to a lesser extent in a portion 58 of the
concave surface 34 represented in FIG. 2 as directly aft of the
leading edge 14. FIG. 2 represents a coating system 62 of a type
noted above as comprising sacrificial and erosion-resistant
coatings, described in more detail below. The coating system 62 may
be disposed over all or any portion of the airfoil surface 32, but
is particularly suited for disposition on the portions 50, 54, and
58 of the airfoil surface 32 that are most susceptible to corrosion
and erosion, as described above.
[0019] The blade 1 is represented in FIG. 2 as having a substrate
60, which may be made from various stainless steels and superalloys
including, but not limited to, Fe-based, Co-based and Ni-based
superalloy compositions. The superalloys may include aluminum
and/or titanium as solutes. Generally, the aluminum and/or titanium
concentrations are low (e.g., less than or equal to about 15 weight
percent (wt %) each). Other optional components include chromium,
molybdenum, cobalt (in Fe-based or Ni-based superalloys), tungsten,
nickel (in Fe-based or Co-based superalloys), rhenium, iron (in
Co-based or Ni-based superalloys), tantalum, vanadium, hafnium,
columbium, ruthenium, zirconium, boron, yttrium, and carbon, each
of which may independently be present in an amount of less than or
equal to about 15 wt %. The substrate 60 of the blade 1 may be made
from various grades of stainless steel, including, but not limited
to, both 300 series and 400 series stainless steels. For example,
the blade 1 may comprise type 450 stainless steel, a martensitic,
age-hardenable alloy having a reported composition of, by weight,
up to 0.05% carbon, up to 1.00% manganese, up to 0.030%
phosphorous, up to 0.030% sulfur, up to 1.00% silicon, 14.00 to
16.00% chromium, 5.00 to 7.00% nickel, 0.50 to 1.00% molybdenum,
1.25 to 1.75% copper, niobium (columbium) in a minimum amount of 8
times that of the percent of carbon, and the balance (approximately
72.14 to 77.14%) iron and impurities.
[0020] The airfoil surface 32 is an outermost surface of the
substrate 60 of the airfoil 10 represented in FIG. 2. FIG. 3
represents the coating system 62 as including a sacrificial coating
64 disposed on the substrate 60 and an erosion-resistant coating 66
disposed on the sacrificial coating 64. Hence, the structure may be
described generally as a blade 1 having the airfoil surface 32,
sacrificial coating 64, and erosion-resistant coating 66, wherein
the sacrificial coating 64 is disposed on the airfoil surface 32
and the erosion-resistant coating 66 is directly disposed on the
sacrificial coating 64. The coating system 62 may have any
thickness that is effective for providing a predetermined amount of
corrosion-resistance and erosion-resistance, including the sum of
those described below for the sacrificial coatings 64 and the
erosion-resistant coatings 66. The coating system 62 preferably
provides suitable corrosion-resistance, particularly with regard to
galvanic and crevice corrosion, and erosion resistance,
particularly with regard to water droplet erosion, to the airfoil
10 at least in the portions 54 and 58 of the concave surface 34,
more preferably over the entire or substantially the entire area of
the concave surface 34, and most preferably over the entire or
substantially the entire area of both of the convex and concave
surfaces 30 and 34.
[0021] Preferably, the sacrificial coating 64 is more anodic than
both the substrate 60 and erosion-resistant coating 66. By more
anodic, it is meant that the electromotive force (emf) or corrosion
potential with respect to a standard thermodynamic reference
potential of the sacrificial coating 64 is more negative than that
of either the substrate 60 or erosion-resistant coating 66 in a
corrosive (reactant) species to which the blade 1 is exposed. These
species may be ingested together with water droplets from the
external environment, or may mix with water droplets that are
deliberately introduced. For example, these species may include
various ionic species, including those comprising, Cl.sup.-,
Br.sup.-, F.sup.-, S.sup.2-, and/or others. Together with the water
droplets, these species are capable of participating in various
electrochemical reactions and thereby causing electrochemical
erosion and corrosion of the airfoil surface 32. By making the
sacrificial coating 64 electrochemically more anodic than either
the airfoil surface 32 or the erosion-resistant coating 66, these
species most likely will preferentially attack the sacrificial
coating 64 rather than the airfoil surface 32.
[0022] Reference herein to the sacrificial coating 64 being
disposed on the airfoil surface 32 means that it is attached and
tightly adherent to this surface, preferably by virtue of chemical
or metallurgical bonding, such that it is able to undergo normal
operating and thermal stresses without exhibiting spallation or
other coating degradation processes. The airfoil surface 32 may be
treated to produce a residual compressive surface stress in order
to reduce the tendency of any cracks or pits (or other features
that might tend to cause a stress riser at the surface) from
propagating from the airfoil surface 32 into the interior of the
airfoil 10. Residual compressive stresses may be imparted to the
airfoil surface 32 by shot peening, laser peening or other
treatments that also produce residual compressive stresses, or
other methods. The coating system 62 may also be disposed so as to
include residual compressive stresses, preferably compressive
stresses that are greater than those of the airfoil surface 32,
more preferably where the airfoil surface 32 includes residual
compressive stresses. For example, the sacrificial coating 64 may
be formed to have a residual compressive stress of about 3792
MPa.
[0023] The sacrificial coating 64 may comprise one or more layers
comprising, for example, Al, Cr, Zn, Al-based alloys, Cr-based
alloys, Zn-based alloys, and/or combinations thereof which are
preferably more anodic than the airfoil surface 32 or the
erosion-resistant coating 66. Alternatively, the sacrificial
coating 64 may comprise various glasses, ceramics, polymers and
composites, in any combination, that include the above-mentioned
metallic materials. For example, the sacrificial coating 64 may
comprise an Al particle polymer composite. These metallic materials
may further be used in particulate or other forms in various paints
and composite materials, including those comprising various
polymeric materials, including metal particle pigmented paints,
such as aluminum particle pigmented paints having an aluminum
content of about 70% or more, by weight.
[0024] The sacrificial layer 64 may be disposed either on the
airfoil surface 32 or over a previously deposited coating system
(not shown), but is particularly suited to being directly disposed
on the airfoil surface 32, as this arrangement places the anodic
material in direct electrical contact with the airfoil surface 32,
thereby improving the likelihood of anodic protection of the
airfoil surface 32. The sacrificial layer 64 may be deposited as a
thin film or thick film layer by any suitable application or
deposition method, including, but not limited to, plating
(electroplating and electroless plating), dipping, spraying,
painting, chemical vapor deposition (CVD), or physical vapor
deposition (PVD), such as EB-PVD, filtered arc deposition, and more
preferably by sputtering. Suitable sputtering techniques include,
but are not limited to, direct current diode sputtering, radio
frequency sputtering, ion beam sputtering, reactive sputtering,
magnetron sputtering and steered arc sputtering. The sacrificial
coating 64 may include a single layer, or may be provided in
multiple layers, including a sacrificial coating 64 that includes a
plurality of different materials as sub-layers disposed in a
contiguous fashion to form the sacrificial coating 64. In a single
layer configuration, the sacrificial coating 64 may have any
suitable thickness needed to provide anodic protection of the
airfoil surface 32, including to obtain a predetermined or design
service life. For example, the thickness of the sacrificial coating
64 in the form of a thick film, such as a metal particle/polymer
matrix paint, may range from about 120 to 730 micrometers. The
thickness of the sacrificial coating 64 deposited using a thin film
deposition method preferably has a higher density than the thick
film sacrificial coatings 64 and may have a thickness in the range
of about 5 to 50 micrometers.
[0025] As an example of a multilayer configuration, the sacrificial
coating 64 may include a conductive undercoat layer and an overcoat
layer disposed thereon of an inorganic binder having a plurality of
ceramic particles and conductive particles embedded therein, as
described in U.S. Pat. Nos. 5,098,797 and 5,260,099. In particular,
the conductive undercoat layer may include a continuous, relatively
thin, sacrificial metal layer, such as a layer of a nickel cadmium
alloy. Such a sacrificial metal layer may be electroplated to a
thickness of about 5 to 10 micrometers, preferably about 7.6
micrometers. Alternately, the conductive undercoat layer may be
provided by flame or plasma spraying techniques known in the art,
or preferably by applying a metallic paint, such as an aluminum
particle/polymer matrix paint. When using the metallic paint, the
airfoil surface 32 may be initially prepared by grit blasting and
then drying, heating to cure and then consolidating the metal
powder in contact with the airfoil surface 32, such as
consolidation by glass bead blasting. Generally, a single
application will be sufficient to produce the conductive undercoat
layer of the metallic paint having a thickness in the range
described above. The overcoat layer is disposed on the conductive
undercoat layer and includes an inorganic matrix binder having a
plurality of ceramic particles and conductive particles embedded
therein. For example, the inorganic matrix binder may include a
phosphate chromate binder having a plurality of aluminum oxide and
chromium oxide ceramic particles and aluminum metal particles
embedded therein. The binder may also include cobalt and other
metal or conductive particles. The overcoat layer may be made using
the methods disclosed in U.S. Pat. No. 3,248,251. The amount of the
embedded metal particles may be selected to make the overcoat layer
more anodic than the airfoil surface 32 or the erosion-resistant
layer 66. The overcoat layer may be deposited in any suitable
thickness. For example, where the inorganic matrix binder is a
phosphate chromate binder having aluminum oxide and chromium oxide
ceramic particles and aluminum metal particles embedded therein,
the thickness of the overcoat layer may be about 3 micrometers or
more.
[0026] As noted above, the erosion-resistant coating 66 of the
coating system 62 may be disposed on the outer surface of the
sacrificial coating 64. The erosion-resistant coating 66 may be one
or more layers comprising an impact-absorbent, erosion-resistant
layer of a polymeric material that is more elastic than the
ceramic-based erosion materials of the prior art. If the
sacrificial coating 64 includes the undercoat and overcoat layers
as described above, such as the phosphate chromate inorganic matrix
binder, the overcoat layer may also provide some erosion-resistance
to the coating system 62 due to the hardness and abrasion
resistance of the embedded ceramic particles; however, the
phosphate chromate ceramic overcoat layer alone is not suitable for
use as the erosion-resistant layer 66, as disclosed herein, because
it does not provide sufficient erosion-resistance owing to its
porous morphology.
[0027] The polymeric material of the erosion-resistant coating 66
is preferably chosen for its ability to absorb and re-emit the
energy of the erosive attack. Other preferred properties include
materials that are sufficiently hydrophobic to shed water, and
materials that are anti-fouling to limit the amount of
water-washing required in a compressor application. Suitable
polymeric compositions include Si-based polymers such as, but not
limited to, siloxanes, silicon alkyds, and flurosilicones, C-based
polymers such as modified bituminous materials, modified tar,
epoxy-based materials, elastomers, for example, polybutadiene,
neoprene, butyl rubber, and the like, and/or combinations thereof.
This may also include an erosion-resistant coating 66 that has
multiple erosion-resistant layers of the same or different
erosion-resistant materials, including those that also include a
primer material layer to promote adherence of the erosion-resistant
coating 66 to the sacrificial coating 64 or to other layers of the
erosion-resistant coating 66. Suitable primer compositions include
most epoxies as well as other materials that promote the adherence
of the layers of the erosion-resistant coating 66.
[0028] Any suitable thickness of a single layer and a multilayer
erosion-resistant coating 66 may be used, so long as it is
effective to provide increased erosion resistance to the airfoil
surface 32. For example, if the erosion-resistant coating 66 is
composed of a single layer of a siloxane-based material, an
effective layer thickness includes a minimum thickness of about 25
to a maximum thickness of about 380 micrometers. Preferably the
single layer thickness is in the range of about 50 to 125
micrometers. The minimum thickness will be that which is effective
to provide erosion-resistance greater than that of the bare airfoil
surface 32, which generally will be a layer thickness sufficient to
insure complete coverage of the airfoil surface 32, including
features such as film cooling holes, etc., while avoiding coating
defects sometimes associated with thin layers, such as pinholes.
The maximum thickness may be any suitable thickness, but is
preferably a thickness that is effective to provide a desired
service life to the airfoil surface 32 in a predetermined operating
environment, while also maintaining a desired level of adherence or
bond strength to the sacrificial coating 64 to which it is
applied.
[0029] The erosion-resistant coating 66 having one or more
polymeric layers may be disposed as a thin film or thick film layer
by any suitable application or deposition method, including airless
spraying, dipping, brushing, high-volume, low-pressure (HVLP)
spraying, or other suitable means.
[0030] While the invention disclosed herein have been described
above with particular reference to an embodiment of a compressor
blade 1, the coating systems of the types described herein may also
be applied to other airfoil surfaces that may be subject to water
droplet erosion or crevice corrosion as described herein.
[0031] Therefore, while the invention has been described in detail
in connection with only a limited number of embodiments, it should
be readily understood that the invention is not limited to such
disclosed embodiments. Rather, the invention can be modified to
incorporate any number of variations, alterations, substitutions or
equivalent arrangements not heretofore described, but which are
commensurate with the spirit and scope of the invention.
Additionally, while various embodiments of the invention have been
described, it is to be understood that aspects of the invention may
include only some of the described embodiments. Accordingly, the
invention is not to be seen as limited by the foregoing
description, but is only limited by the scope of the following
claims.
* * * * *