U.S. patent application number 11/925360 was filed with the patent office on 2009-02-19 for layered corrosion resistant coating for turbine blade environmental protection.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. Invention is credited to Brian Thomas Hazel, Bangalore Aswatha Nagaraj.
Application Number | 20090047135 11/925360 |
Document ID | / |
Family ID | 37772933 |
Filed Date | 2009-02-19 |
United States Patent
Application |
20090047135 |
Kind Code |
A1 |
Nagaraj; Bangalore Aswatha ;
et al. |
February 19, 2009 |
LAYERED CORROSION RESISTANT COATING FOR TURBINE BLADE ENVIRONMENTAL
PROTECTION
Abstract
The present invention is a gas turbine engine turbine blade
comprising an airfoil section having at least an exterior surface,
a platform section having an exterior surface, an under platform
section having an exterior surface, and a dovetail section having
an exterior surface. The blade further comprises a corrosion
resistant coating on a surface of a turbine blade section selected
from the group consisting of the exterior surface of the under
platform section, the exterior surface of the dovetail section, and
combinations thereof, the corrosion resistant coating comprising a
particulate corrosion resistant component comprising from about 5
weight percent to about 100 weight percent corrosion resistant
non-alumina particulates having a CTE greater than that of alumina
particulates and balance alumina particulates, and a binder
component. The present invention also includes methods for making
such a gas turbine engine blade.
Inventors: |
Nagaraj; Bangalore Aswatha;
(West Chester, OH) ; Hazel; Brian Thomas; (West
Chester, OH) |
Correspondence
Address: |
MCNEES WALLACE & NURICK LLC
100 PINE STREET, P.O. BOX 1166
HARRISBURG
PA
17108-1166
US
|
Assignee: |
GENERAL ELECTRIC COMPANY
Schenectady
NY
|
Family ID: |
37772933 |
Appl. No.: |
11/925360 |
Filed: |
October 26, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11266857 |
Nov 4, 2005 |
7311940 |
|
|
11925360 |
|
|
|
|
Current U.S.
Class: |
416/241R |
Current CPC
Class: |
Y02T 50/67 20130101;
C23C 30/00 20130101; Y02T 50/60 20130101; F01D 5/288 20130101; C23C
24/08 20130101; F05D 2300/50212 20130101; Y02T 50/671 20130101;
C23C 26/00 20130101 |
Class at
Publication: |
416/241.R |
International
Class: |
F01D 5/14 20060101
F01D005/14 |
Claims
1. A gas turbine engine turbine blade comprising: an airfoil
section having at least an exterior surface; a platform section
having an exterior surface; an under platform section having an
exterior surface; a dovetail section having an exterior surface;
and a corrosion resistant coating on a surface of a turbine blade
section selected from the group consisting of the exterior surface
of the under platform section, the exterior surface of the dovetail
section, and combinations thereof, the corrosion resistant coating
comprising: a particulate corrosion resistant component comprising
from about 5 weight percent to about 100 weight percent corrosion
resistant non-alumina particulates having a CTE greater than that
of alumina particulates and balance alumina particulates; and a
binder component.
2. A gas turbine engine turbine blade comprising: an airfoil
section having at least an exterior surface; a platform section
having an exterior surface; an under platform section having an
exterior surface; a dovetail section having an exterior surface;
and a corrosion resistant coating on a surface of a turbine blade
section selected from the group consisting of the exterior surface
of the under platform section, the exterior surface of the dovetail
section, and combinations thereof, the corrosion resistant coating
comprising a plurality of layers, with at least one lower layer
adjacent to the exterior surface and at least one upper layer
adjacent the at least one lower layer, wherein the at least one
lower layer comprises: a particulate corrosion resistant component
comprising from about 5 weight percent to about 100 weight percent
corrosion resistant non-alumina particulates having a CTE greater
than that of alumina particulates and balance alumina particulates;
and a binder component; and wherein the at least one upper layer
comprises: a particulate corrosion component comprising a higher
weight percent of alumina particulates than the lower layer; and a
binder component.
3. The gas turbine engine turbine blade of claim 1, wherein the
corrosion resistant coating further comprises a sealant layer
adjacent to the corrosion resistant coating.
4. The gas turbine engine blade of claim 1, wherein the non-alumina
corrosion resistant particulates comprise a ceramic selected from
the group consisting of zirconia, zirconia stabilized with yttria,
zirconia stabilized with a rare earth oxide, and combinations
thereof.
5. The gas turbine engine turbine blade of claim 2, wherein the
corrosion resistant coating further comprises a sealant layer
adjacent to the at least one upper layer.
6. The gas turbine engine blade of claim 2, wherein the non-alumina
corrosion resistant particulates comprise a ceramic selected from
the group consisting of zirconia, zirconia stabilized with yttria,
zirconia stabilized with a rare earth oxide, and combinations
thereof.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. Utility application
Ser. No. 11/266,857, Attorney Docket No. 136493 (07783-0225-01),
filed on Nov. 4, 2005 entitled "LAYERED CORROSION RESISTANT COATING
FOR TURBINE BLADE ENVIRONMENTAL PROTECTION", which is incorporated
herein by reference in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates generally to a corrosion
resistant coating and more particularly to a method of applying a
corrosion resistant coating to an under platform surface of a gas
turbine engine turbine blade.
BACKGROUND OF THE INVENTION
[0003] In an aircraft gas turbine engine, air is drawn into the
front of the engine, compressed by a shaft-mounted compressor, and
mixed with fuel. The mixture is burned, and the hot exhaust gases
are passed through a turbine mounted on the same shaft. The flow of
combustion gas turns the turbine by impingement against the airfoil
section of the turbine blades, which turns the shaft and provides
power to the compressor. The hot exhaust gases flow from the back
of the engine, driving it and the aircraft forward. The hotter the
combustion and exhaust gases, the more efficient is the operation
of the jet engine. Thus, there is incentive to raise the combustion
gas temperature.
[0004] The compressors and turbine of the turbine engine can
comprise turbine disks (sometimes termed "turbine rotors") or
turbine shafts, as well as a number of blades mounted to the
turbine disks/shafts and extending radially outwardly therefrom
into the gas flow path, and rotating. Also included in the turbine
engine are rotating, as well as static, seal elements that channel
the airflow used for cooling certain components such as turbine
blades and vanes. The airflow channeled by these rotating, as well
as static, seal elements carry corrodant deposits to the non-gas
path sides of turbine blades. As the maximum operating temperature
of the turbine engine increases, the turbine blades are subjected
to higher temperatures. As a result, oxidation and corrosion of the
turbine blades have become of greater concern.
[0005] Metal salts such as alkaline sulfate, sulfites, chlorides,
carbonates, oxides, and other corrodant salt deposits resulting
from ingested dirt, fly ash, volcanic ash, concrete dust, sand, sea
salt, etc. are a major source of the corrosion, but other elements
in the bleed gas environment can also accelerate the corrosion.
Alkaline sulfate corrosion in the temperature range and atmospheric
region of interest results in pitting of the turbine blade
substrate at temperatures typically starting around 1200.degree. F.
(649.degree. C.). This pitting corrosion has been shown to occur on
turbine blades, primarily the region beneath platforms of turbine
blades. The oxidation and corrosion damage can lead to failure or
premature removal and replacement of the turbine blades unless the
damage is reduced or repaired.
[0006] Turbine blades for use at the highest operating temperatures
are typically made of nickel-base superalloys selected for good
elevated temperature toughness and fatigue resistance. In addition,
the turbine blade alloys are coated with environmental coatings to
primarily protect the turbine airfoil and platform structures for
oxidation and corrosion. These coatings may additionally be
deposited on the under platform region of the turbine blade.
Typical environmental coatings in wide use include MCrAlX overlay
coatings (where M is iron, cobalt and/or nickel, and X is yttrium
or another rare earth element), and diffusion coatings that contain
aluminum intermetallics, predominantly beta-phase nickel aluminide
(.beta.NiAl) and platinum aluminides (PtAl). These superalloys and
the existing environmental coatings used have resistance to
oxidation and corrosion damage, but that resistance is not
sufficient to protect them at sustained operating temperatures now
being reached in gas turbine engines.
[0007] Corrosion resistant coating compositions have been suggested
for use with various gas turbine components. These include aqueous
corrosion resistant coating compositions comprising
phosphate/chromate binder systems and aluminum/alumina particles.
See, for example, U.S. Pat. No. 4,606,967 (Mosser), issued Aug. 19,
1986 (spheroidal aluminum particles); and U.S. Pat. No. 4,544,408
(Mosser et al), issued Oct. 1, 1985 (dispersible hydrated alumina
particles). Corrosion resistant diffusion coatings can also be
formed from chromium, or from the respective oxide (i.e., chromia).
See, for example, commonly assigned U.S. Pat. No. 6,283,715
(Nagaraj et al), issued Sep. 4, 2001 (chromium diffusion coating).
A number of corrosion resistant coatings have also been
specifically considered for use on turbine disk/shaft and seal
elements. See, for example, U.S. Patent Application 2004/0013802 A1
(Ackerman et al), published Jan. 22, 2004 (metal-organic chemical
vapor deposition of aluminum, silicon, tantalum, titanium or
chromium oxide on turbine disks and seal elements to provide a
protective coating). These prior corrosion resistant coatings have
a number of disadvantages when used with turbine blades, including:
(1) possibly adversely affecting the fatigue life of the turbine
blade elements, especially when these prior coatings diffuse into
the underlying metal substrate; (2) potential coefficient of
thermal expansion (hereinafter, "CTE") mismatches between the
coating and the underlying metal substrate that can make the
coating more prone to spalling; and (3) more complicated and
expensive processes (e.g., chemical vapor deposition) for applying
the corrosion resistant coating to the metal substrate.
[0008] What is needed are coatings and coating compositions for
turbine blades that: (1) provide corrosion resistance, especially
at higher or elevated temperatures; (2) do not affect other
mechanical properties of the underlying metal substrate or
potentially causing other undesired effects such as spalling; (3)
can be formed by relatively uncomplicated and inexpensive methods;
(4) can allow for non-destructive evaluation of the underlying
substrate during engine overhaul; and (5) can be reapplied or
refurbished for continued engine operation. The present invention
provides these and other related advantages.
SUMMARY OF THE INVENTION
[0009] An embodiment of the present method for coating on under
platform section of a gas turbine engine blade, the method
comprising the step of providing a gas turbine blade comprising a
superalloy selected form the group consisting of nickel-base
superalloys, cobalt-base superalloys, iron-base superalloys, and
combinations thereof, the blade further comprising an airfoil
section having at least an exterior surface, a platform section
having an exterior surface, an under platform section having an
exterior surface, and a dovetail section having an exterior
surface. The method further comprises the step of masking a
preselected portion of the gas turbine blade leaving the exterior
surface of a non-masked section selected from the group consisting
of the under platform section, the dovetail section, and
combinations thereof, unmasked. The method further comprises
applying a layer of corrosion resistant coating composition, the
composition comprising a glass-forming binder and corrosion
resistant particulates to the exterior surface of the non-masked
section, the particulates comprising from about 5 weight percent to
about 100 weight percent non-alumina corrosion resistant
particulates having a CTE greater than that of the alumina
particulates and balance alumina particulates. The method further
comprises curing the layer of corrosion resistant coating
composition to form a corrosion resistant coating layer. The method
further comprises removing the maskant.
[0010] Another embodiment of the present invention is a gas turbine
engine turbine blade comprising an airfoil section having at least
an exterior surface, a platform section having an exterior surface,
an under platform section having an exterior surface, and a
dovetail section having an exterior surface. The blade further
comprises a corrosion resistant coating on a surface of a turbine
blade section selected from the group consisting of the exterior
surface of the under platform section, the exterior surface of the
dovetail section, and combinations thereof, the corrosion resistant
coating comprising a particulate corrosion resistant component
comprising from about 5 weight percent to about 100 weight percent
corrosion resistant non-alumina particulates having a CTE greater
than that of alumina particulates and balance alumina particulates,
and a binder component.
[0011] Yet another embodiment of the present invention is a gas
turbine engine turbine blade comprising an airfoil section having
at least an exterior surface, a platform section having an exterior
surface, an under platform section having an exterior surface, and
a dovetail section having an exterior surface. The blade further
comprises a corrosion resistant coating on a surface of a turbine
blade section selected from the group consisting of the exterior
surface of the under platform section, the exterior surface of the
dovetail section, and combinations thereof. The corrosion resistant
coating comprises a plurality of layers, with at least one lower
layer adjacent to the exterior surface and at least one upper layer
adjacent the at least one lower layer. The at least one lower layer
comprises a particulate corrosion resistant component comprising
from about 5 weight percent to about 100 weight percent corrosion
resistant non-alumina particulates having a CTE greater than that
of alumina particulates and balance alumina particulates and a
binder component. The at least one upper layer comprises a
particulate corrosion component comprising a higher weight percent
of alumina particulates than the lower layer and a binder
component.
[0012] An advantage of the present invention is that the corrosion
resistant coating of the present invention will provide corrosion
resistance at elevated temperatures.
[0013] Another advantage of the present invention is that the
coating of the present invention does not affect other mechanical
properties of the underlying metal substrate.
[0014] Another advantage of the present invention is that that
corrosion resistant coating of the present invention does not cause
other undesired effects such as spalling.
[0015] Yet another advantage of the present invention is that the
corrosion resistant coating of the present invention may be applied
to a gas turbine blade by relatively uncomplicated and inexpensive
methods.
[0016] Yet another advantage of the present invention is that the
corrosion resistant coating of the present invention allows
non-destructive testing of the underlying substrate during engine
overhaul.
[0017] Yet another advantage of the present invention is that the
corrosion resistant coating of the present invention can be
reapplied or refurbished for continued engine operation.
[0018] Other features and advantages of the present invention will
be apparent from the following more detailed description of the
preferred embodiment, taken in conjunction with the accompanying
drawings which illustrate, by way of example, the principles of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a process flow chart illustrating the application
of the corrosion resistant coating of the present invention as a
single-layer corrosion resistant coating.
[0020] FIG. 2 is a process flow chart illustrating the application
of the corrosion coating of the present invention as a
multiple-layer corrosion resistant coating.
[0021] FIG. 3 is a perspective view of an embodiment of a turbine
blade coated with the corrosion resistant coating of the present
invention.
[0022] FIG. 4 is a schematic view of a single-layer corrosion
resistant coating of the present invention deposited on the under
platform substrate of the turbine blade.
[0023] FIG. 5 is a schematic view similar to FIG. 4 of a
single-layer corrosion resistant coating of the present invention
with an additional outer layer.
[0024] FIG. 6 is a schematic view similar to FIG. 4 of a
multiple-layer corrosion resistant coating of the present invention
deposited on the under platform substrate of the turbine blade.
[0025] FIG. 7 is a schematic view similar to FIG. 4 of another
multiple-layer corrosion resistant coating of the present invention
deposited on the under platform substrate of the turbine blade with
an additional outer layer.
DETAILED DESCRIPTION OF THE INVENTION
[0026] As used herein, the term "particulate" refers to a particle,
powder, flake, etc., that inherently exists in a relatively small
form (e.g., a size of about 50 microns or less) or can be formed
by, for example, grinding, shredding, fragmenting, pulverizing or
otherwise subdividing a larger form of the material into a
relatively small form.
[0027] As used herein, the term "unimodal particle size
distribution" refers to a particle size distribution comprising one
particle size fraction. When graphically plotted, a unimodal
particle size distribution has essentially a single peak.
[0028] As used herein, the term "bimodal particle size
distribution" refers to a particle size distribution that comprises
a smaller particle size fraction and a larger particle size
fraction. When graphically plotted, a bimodal particle size
distribution has essentially two distinct peaks.
[0029] As used herein, the term "polymodal particle size
distribution" refers to a particle size distribution that comprises
three or more particle size fractions. When graphically plotted, a
polymodal particle size distribution has three or more distinct
peaks.
[0030] As used herein, the term "alumina particulates" refers to
particulates comprising compounds, compositions, etc., of aluminum
oxide typically having the formula Al.sub.2O.sub.3, including
unhydrated and hydrated forms.
[0031] As used herein, the term "corrosion resistant non-alumina
particulates" refers to particulates that provide corrosion
resistance and comprise a metal (other than solely aluminum), a
ceramic or combination thereof that is substantially free of
alumina.
[0032] As used herein, the term "substantially free" means the
indicated compound, material, component, etc., is minimally present
or not present at all, e.g., at a level of about 0.5% or less, more
typically at a level of about 0.1% or less, unless otherwise
specified.
[0033] As used herein, the term "corrosion resistant particulate
component" refers to a component comprising corrosion resistant
non-alumina particulates, with or without alumina particulates. The
particular level and amount of corrosion resistant non-alumina
particulates and alumina particulates present in the corrosion
resistant particulate component can be varied depending on the CTE
properties desired for the resultant corrosion resistant coating,
whether the corrosion resistant coating comprises a single layer or
a plurality of layers, the thickness of the coating, the particle
size distribution of the corrosion resistant non-alumina
particulates and the alumina particulates, etc. The non-alumina
particulates have a CTE greater than that of alumina particles. The
corrosion resistant particulate component comprises from about 5 to
100% corrosion resistant non-alumina particulates with balance
alumina particulates, preferably from about 25 to 100% corrosion
resistant non-alumina particulates with balance alumina
particulates and, more preferably from about 50 to 100% corrosion
resistant non-alumina particulates balance alumina particulates and
can consist essentially of corrosion resistant non-alumina
particulates, e.g., about 100% corrosion resistant non-alumina
particulates. The particulates comprising the corrosion resistant
particulate component can have particle sizes in the range of from
about 0.01 to about 50 microns, more typically in the range of from
about 0.1 to about 25 microns and can comprise particulates having
unimodal, bimodal or polymodal particle size distributions. When
the corrosion resistant particulate component comprises corrosion
resistant non-alumina particulates and alumina particulates, a
bimodal particle size distribution can be desirable to provide a
greater solids packing density for the particulate component. For
bimodal particle size distributions, the larger particle size
fraction can comprise the non-alumina particulates, while the
smaller particulate size fraction can comprise the alumina
particulates, and vice versa.
[0034] As used herein, the term "metal" can refer to a single metal
or a metal alloy, i.e., a blend of at least two metals (e.g.,
aluminum alloys). Metals can include chromium, zirconium, nickel,
cobalt, iron, titanium, yttrium, magnesium, platinum group metals
(e.g., platinum, palladium, rhodium, iridium, etc.), hafnium,
silicon, tantalum, etc., alloys of any of these metals, and alloys
of any of these metals with aluminum, e.g., overlay metal
alloys.
[0035] As used herein, the term "rare earth element" can refer to a
single rare earth element or a combination of rare earth elements.
Rare earth elements can include lanthanum, cerium, praseodymium,
neodymium, samarium, europium, gadolinium, terbium, dysprosium,
holmium, erbium, thulium, ytterbium, lutetium and combinations
thereof.
[0036] As used herein, the term "rare earth oxide" refers to an
oxide(s) of a rare earth element.
[0037] As used herein, the term "ceramic" refers to an oxide,
carbide, nitride, etc., of a metal. Ceramics suitable for use
herein include oxides, carbides, nitrides, etc., of any of the
metals (other than solely aluminum) referred to herein,
combinations of such oxides, carbides, nitrides, etc., including,
but not limited to zirconia and phase-stabilized zirconias (i.e.,
various metal oxides, for example, yttrium oxides blended with
zirconia), such as yttria-stabilized zirconias, calcia-stabilized
zirconias, scandia-stabilized zirconias, magnesia-stabilized
zirconias, zirconias stabilized by any rare earth oxide, for
example rare earth oxide stabilized zirconia as described in U.S.
Pat. No. 6,025,078 (Rickerby et al.), issued Feb. 15, 2000, which
is hereby incorporated by reference in its entirety, etc., as well
as mixtures of such stabilized zirconias. Suitable
yttria-stabilized zirconias can comprise from about 1 to about 65%
yttria (based on the combined weight of yttria and zirconia), and
more preferably from about 3 to about 10% yttria. Other suitable
ceramics for use herein include titania, ceria,
Y.sub.3Al.sub.5O.sub.12, hafnia, and hafnia stabilized by any rare
earth oxide, lanthanum hexyluminate, and other metal aluminates,
chromium carbide (Cr.sub.2C.sub.3), etc.
[0038] As used herein, the term "overlay metal alloy" refers to
metal alloys having the formula MCr, MAl, MCrAl, MCrAlX, MCrX, or
MAlX, wherein M is nickel, cobalt, iron, etc., or an alloy thereof
and wherein X is hafnium, zirconium, yttrium, tantalum, platinum,
palladium, rhenium, silicon, etc., or a combination thereof.
Typically, the overlay metal alloys used herein are MCrAlX alloys,
and more typically wherein M is nickel or a nickel-cobalt alloy and
wherein X is yttrium (i.e., Y).
[0039] As used herein, the term "corrosion resistant coating"
refers to coatings that, after curing of the deposited corrosion
resistant coating of this invention, comprise at least one layer
adjacent to the metal substrate having an amorphous, glassy matrix
and having embedded therein, encapsulated therein, enclosed
thereby, or otherwise adhered thereto, particulates from the
corrosion resistant particulate component. Corrosion resistant
coatings of this invention can provide resistance against corrosion
caused by various corrodants, including metal (e.g., alkaline)
sulfates, sulfites, chlorides, carbonates, oxides, and other
corrodant salt deposits resulting from ingested dirt, fly ash,
volcanic ash, concrete dust, sand, sea salt, etc., at temperatures
typically of at least about 1000.degree. F. (538.degree. C.), more
typically at least about 1200.degree. F. (649.degree. C.). The
corrosion resistant coatings of this invention can be homogeneous
or substantially homogeneous throughout in the terms of the
composition of the particulate and binder components, or can
comprise a discrete layer(s) adjacent to the metal substrate that
comprises a homogenous or substantially homogeneous composition of
the particulate and binder components. For example, the corrosion
resistant coatings of this invention can be a single layer
comprising non-alumina particulates throughout that have a CTE
greater than that of alumina, or can be a plurality of layers of
differing composition, e.g., an inner layer adjacent to the metal
substrate that comprises non-alumina particulates having a CTE
greater than that of alumina, an intermediate layer that comprises
a higher level of alumina particulates, e.g., a level of alumina
particulates such that the CTE is not measurably different from
that of alumina, and an outer layer that consists essentially of a
composition that is similar to a glass-forming binder component but
without particulates, e.g., a sealant composition that forms a
glassy top coat.
[0040] As used herein, the term "glass-forming binder component"
refers to a component comprising a typically inorganic compound,
composition, etc., that, when cured, forms an amorphous, glassy
matrix to which the particulates in the particulate component are
embedded in, are encapsulated in, are enclosed by, or otherwise
adhered to. Binder components suitable for use herein typically
comprise a phosphate binder, with or without other binder
materials. These phosphate binders can be in the form of phosphoric
acid or more typically the respective phosphate
compounds/compositions, including orthophosphates, pyrophosphates,
etc. These phosphate compounds/compositions can be monobasic,
dibasic, tribasic or any combination thereof. Phosphate-containing
binder components can comprise one or more metal phosphates,
including aluminum phosphates, magnesium phosphates, chromium
phosphates, zinc phosphates, iron phosphates, lithium phosphates,
calcium phosphates, etc, or any combination thereof. Typically, the
phosphate-containing binder component comprises an aluminum
phosphate, a magnesium phosphate, a chromium phosphate, or a
combination thereof. The phosphate-containing binder component can
optionally comprise other binder material, including one or more
chromates, molybdates, etc. See, for example, U.S. Pat. No.
3,248,249 (Collins, Jr.), issued Apr. 26, 1966; U.S. Pat. No.
3,248,251 (Allen), issued Apr. 26, 1966; U.S. Pat. No. 4,889,858
(Mosser), issued Dec. 26, 1989; U.S. Pat. No. 4,975,330 (Mosser),
issued Dec. 4, 1990, all of which are incorporated herein by
reference in their entireties. The phosphate-containing binder
component can also be substantially free of other binder materials,
e.g., a substantially chromate free phosphate-containing binder
component. See, for example, U.S. Pat. No. 6,368,394 (Hughes et
al), issued Apr. 9, 2002 (substantially chromate free phosphate
binder component), which is incorporated herein by reference in its
entirety.
[0041] As used herein, the term "liquid carrier component" refers
to any carrier component that is liquid at ambient temperatures and
in which the corrosion resistant particulate component and
glass-forming binder component is typically carried in, dispersed
in, dissolved in, etc. Liquid carrier components include aqueous
systems (e.g., comprising water), organic systems (e.g., comprising
alcohols such as ethanol, propanol, isopropanol, etc., other liquid
organic materials or solvents such as ethylene glycol, acetone,
etc.) or any combination thereof. These liquid carrier components
can comprise other optional materials such as surfactants, buffers,
etc. Aqueous carrier components can consist essentially of water,
i.e., is substantially free of other optional materials, but more
typically comprises other optional materials such as compatible
organic solvents, surfactants, etc. Suitable surfactants for use in
aqueous carrier components can include nonionic surfactants,
anionic surfactants, cationic surfactants, amphoteric surfactants,
zwitterionic surfactants, or any combination thereof. Illustrative
examples of surfactants suitable for use herein include ethoxylated
alkyl phenols or aliphatic alcohols, nonionic tertiary glycols,
cationic secondary and tertiary amines of the polyoxy cocamine
type, quaternary amines, as well as sodium heptadecyl sulfate,
sodium tetradecyl sulfate and sodium 2-ethylhexyl sulfate. The
inclusion of surfactants can be for the purpose of improving the
wettability of the particulate component, reducing the surface
tension of the corrosion resistant coating composition, promoting
the formation of improved smoothness in the resultant corrosion
resistant coating, etc.
[0042] As used herein, the term "corrosion resistant coating
composition" refers to any coating composition of this invention
comprising the corrosion resistant particulate component, the
glass-forming binder component, optionally a liquid carrier
component, etc., and which is used to form at least one layer of
the corrosion resistant coating of this invention that is adjacent
to the metal substrate. For corrosion resistant coating
compositions of this invention, the ratio of the corrosion
resistant particulate component to glass-forming binder component
is typically in the range from about 0.1 to about 10, more
typically in the range of from about 0.5 to about 5. The optional
liquid carrier component, when included, typically comprises the
balance of the corrosion resistant coating composition of this
invention. The corrosion resistant coating compositions of this
invention can be formulated as flowable solids (e.g., flowable
powders), can be formulated as cast tapes comprising a blend,
mixture or other combination of the particulate and binder
components, with or without a supporting structure such as a film,
strip, etc., or can be formulated as liquids. The corrosion
resistant coating compositions of this invention can comprise other
optional components such as colorants or pigments, viscosity
modifying or controlling agents, etc. Typically, the corrosion
resistant coating compositions of this invention are formulated as
liquid compositions. The liquid corrosion resistant coating
compositions of this invention can be of any desired consistency,
flowability, viscosity, etc., including thixotropic or
non-thixotropic compositions. The aqueous corrosion resistant
coating compositions of this invention usually have an acidic pH
(i.e., below about 7). For example, for aqueous corrosion resistant
coating compositions comprising a phosphate-containing binder
component, the pH is typically in the range of from about 0 to
about 3, and more typically in the range of from about 1.5 to about
3.
[0043] As used herein, the term "curing" refers to any treatment
condition or combination of treatment conditions that causes the
corrosion resistant coating composition to thereby form the
corrosion resistant coating. Typically, curing occurs by heating
the corrosion resistant coating composition at a temperature of at
least about 250.degree. F. (121.degree. C.), more typically at a
temperature of at least about 500.degree. F. (260.degree. C.).
[0044] As used herein, the term "CTE" refers to the coefficient of
thermal expansion of a material, and is referred to herein in units
of 10.sup.-6/.degree. F. For example, alumina which has a
coefficient of thermal expansion of about 4 to
5.times.10.sup.-6/.degree. F. at about 1200.degree. F. (649.degree.
C.) is referred to herein as having a CTE of about 4 to 5.
[0045] As used herein, the term "CTE greater than alumina" refers
to a CTE of the non-alumina particulate that is measurably greater
than that of the CTE of the alumina particulate at the same or
similar reference temperature. Typically the CTE of the non-alumina
particulate is at least about 0.2 greater, more typically, at least
about 0.5 greater than that of the CTE of the alumina
particulate.
[0046] As used herein, the term "comprising" means various
particulates, materials, coatings, compositions, components,
layers, steps, etc., can be conjointly employed in the present
invention. Accordingly, the term "comprising" encompasses the more
restrictive terms "consisting essentially of" and "consisting
of."
[0047] All amounts, parts, ratios and percentages used herein are
by weight unless otherwise specified.
[0048] Referring now to FIG. 1 there is shown the method of the
present invention for applying a corrosion resistant coating to the
surface of an under platform section of a gas turbine engine
turbine blade. As shown in FIG. 1, in one embodiment of the method
of the present invention, the initial step 100 is the provision of
a gas turbine engine blade having an under platform exterior
surface. As shown in FIG. 3, an exemplary gas turbine engine blade
10 has several sections, including a airfoil section 12, a platform
section 14, an under platform section 16, and a dovetail section
18. Initially, the under platform metal substrate 40, shown in
FIGS. 4-5, is uncoated.
[0049] The metal substrate 40 of the gas turbine engine blade 10
can comprise any of a variety of metals, or more typically metal
alloys, including those based on nickel, cobalt and/or iron alloys.
Substrate 40 typically comprises a superalloy based on nickel,
cobalt and/or iron. Such superalloys are disclosed in various
references, such as, for example, commonly assigned U.S. Pat. No.
6,074,602 (Wuskusick et al.), issued Jun. 13, 2000, which is
incorporated by reference herein in its entirety. The substrate 40
may also be an aluminide bond coat as known in the art.
[0050] Turbine blade substrate 40 more typically comprises a
nickel-based alloy, and particularly a nickel-based superalloy,
that has more nickel than any other element. The nickel-based
superalloy can be strengthened by the precipitation of gamma prime
or a related phase. A nickel-based superalloy for which the
corrosion resistant coating of this invention is particularly
useful is available by the trade name Rene N5, having a nominal
composition in weight percent of about 7.5 percent cobalt, about
7.0 percent chromium, about 1.5 percent molybdenum, about 5 percent
tungsten, about 3 percent rhenium, about 6.5 percent tantalum,
about 6.2 percent aluminum, about 0.15 percent hafnium, about 0.05
percent carbon, about 0.004 percent boron, about 0.01 percent
yttrium, balance nickel and incidental impurities.
[0051] The next step 105 is the masking of a preselected portion of
the turbine blade 10, wherein the portion masked is the portions of
the blade 10 that would not benefit from the roughening and
application of the corrosion resistant coating. The next step 110
is roughening the under platform exterior surface 42 to make the
surface 42 more receptive to the application of the coating of the
present invention. Such roughening includes chemical and/or
mechanic pretreatment. Suitable pretreatment methods include grit
blasting, with or without masking of surfaces that are not to be
subjected to grit blasting (see U.S. Pat. No. 5,723,078 to Nagaraj
et al., issued Mar. 3, 1998, especially col. 4, lines 46-66, which
is incorporated by reference in its entirety), micromachining,
laser etching (see U.S. Pat. No. 5,723,078 to Nagaraj et al.,
issued Mar. 3, 1998, especially col. 4, line 67 to col. 5, line 3
and 14-17, which is incorporated by reference in its entirety),
treatment with chemical etchants such as those containing
hydrochloric acid, hydrofluoric acid, nitric acid, ammonium
bifluorides and mixtures thereof, (see, for example, U.S. Pat. No.
5,723,078 to Nagaraj et al., issued Mar. 3, 1998, especially col.
5, lines 3-10; U.S. Pat. No. 4,563,239 to Adinolfi et al., issued
Jan. 7, 1986, especially col. 2, line 67 to col. 3, line 7; U.S.
Pat. No. 4,353,780 to Fishter et al., issued Oct. 12, 1982,
especially col. 1, lines 50-58; and U.S. Pat. No. 4,411,730 to
Fishter et al., issued Oct. 25, 1983, especially col. 2, lines
40-51, all of which are hereby incorporated by reference in their
entireties), treatment with water under pressure (i.e., water jet
treatment), with or without loading with abrasive particles, as
well as various combinations of these methods. Typically, the
surface 42 of metal substrate 40 is pretreated by grit blasting
where surface 42 is subjected to the abrasive action of silicon
carbide particles, steel particles, alumina particles or other
types of abrasive particles. These particles used in grit blasting
are typically alumina particles and typically have a particle size
of from about 600 to about 35 mesh (from about 25 to about 500
micrometers), more typically from about 360 to about 35 mesh (from
about 35 to about 500 micrometers).
[0052] The next step 115 is depositing a layer of corrosion
resistant coating composition on the surface 42 of the metal
substrate 40. The corrosion resistant coating composition is
disclosed in U.S. patent application Ser. No. 11/011,695, filed
Dec. 15, 2004, entitled "CORROSION RESISTANT COATING COMPOSITION,
COATED TURBINE COMPONENT AND METHOD FOR COATING SAME", which is
incorporated by reference herein in its entirety. The corrosion
resistant coating composition can be deposited in solid form, e.g.,
as a flowable solid, as a cast tape (e.g., a cast tape formed as a
layer or plurality layers of particulates adhered together as a
coherent mass or matrix by the binder, with or without a supporting
structure such as a film, strip, etc.), etc., to provide a solid
uncured layer of the composition comprising the corrosion resistant
particulates and binder component. More typically, the coating
composition is deposited as a liquid, e.g., an aqueous coating
composition. Liquid corrosion resistant coating compositions of
this invention can be deposited on substrate 40 by any manner of
application for depositing liquids including pouring, flowing,
dipping, spraying, rolling, etc., to provide an uncured layer of
the composition comprising the particulates and binder component.
In a preferred embodiment, the non-alumina corrosion resistant
particulates are selected from the group consisting of an overlay
metal alloy, zirconia, yttria-stabilized zirconia, zirconia
stabilized with a rare earth oxide and combinations thereof. In a
more preferred embodiment, the non-alumina corrosion resistant
particulates are selected from the group consisting of NiCrAlY,
CoCrAlY, zirconia, yttria-stabilized zirconia, and combinations
thereof.
[0053] The next step 120 is curing the deposited coating
composition at a temperature that causes the corrosion resistant
particulate component (i.e., non-alumina particulates, plus any
alumina particulates) and glass-forming binder component to form
the layer of the corrosion resistant coating 52 adjacent to metal
substrate 40 that comprises an amorphous, glassy matrix of binder
to which the particulates in the particulate component are embedded
in, encapsulated in, enclosed by, or otherwise adhered to. This
curing is typically accomplished by heating to a temperature of at
least about 250.degree. F. (121.degree. C.), more typically at
least about 500.degree. F. (260.degree. C.) to form corrosion
resistant coating 52. If any liquid carrier component is present in
the deposited coating composition, the liquid carrier component is
evaporated and/or vaporized during the step of curing 120. As shown
in FIG. 4, when no sealant layer is added to the surface 54, then
the surface 54 of coating 52 is the surface 32 of under platform
corrosion resistant coating, shown generally as 50. In such as
case, coating 52 can be formed up to a thickness of about 10 mils
(254 microns), and typically has a thickness in the range of from
about 0.1 to about 5 mils (from about 3 to about 127 microns), more
typically from about 0.2 to about 4 mils (from about 5 to about 102
microns).
[0054] The next optional step 125 is applying a sealant composition
layer to the surface of the cured corrosion resistant coating layer
54. This outer sealant composition layer can comprise a particulate
component, but is typically substantially free of particulates.
Typically, the upper sealant composition layer is formed from a
sealant composition or a composition that consists essentially of,
or entirely of, a glass-forming binder component (i.e., is
substantially free of particulates). Such outer glassy sealant
layers can be formed from commercially available sealant products,
for example, Alseal 598 (from Coatings for Industry, Inc. of
Souderton, Pa.), SermaSeal TCS (from Sermatech International of
Pottstown, Pa.), etc.
[0055] The next optional step 130 is curing the sealant composition
layer to form a glassy outer sealant layer 56. This curing is
typically accomplished by heating the sealant composition layer to
a temperature of at least about 250.degree. F. (121.degree. C.),
more typically at least about 500.degree. F. (260.degree. C.) to
form the upper sealant layer 56 of corrosion resistant coating. If
any liquid carrier component is present in the sealant composition
later, the liquid carrier component is evaporated and/or vaporized
during the step of curing 120. An embodiment of a corrosion
resistant coating of this invention comprising a single corrosion
resistant coating layer 54 and an upper sealant layer 58 is shown
generally as 56 in FIG. 5. Outer layer 58 is also typically thinner
than the underlying layer 52, especially when substantially free of
particulates. As shown in FIG. 5, when a sealant layer 58 is added
to the surface 54, then the surface 60 of the glassy outer sealant
layer 58 is the surface 32 of under platform corrosion resistant
coating 56. In such a case, coating 58 can be formed up to a
thickness of about 10 mils (254 microns), and typically has a
thickness in the range of from about 0.1 to about 5 mils (from
about 3 to about 127 microns), more typically from about 0.2 to
about 4 mils (from about 5 to about 102 microns). Typically, outer
layer 58 has a thickness of from about 0.01 to about 2 mils (from
about 0.3 to about 51 microns), more typically from about 0.1 to
about 1 mils (from about 3 to about 25 microns). The final step 135
is removing the maskant as known in the art.
[0056] In another embodiment of the present invention as shown in
FIG. 2, the first step 200 is the provision of a gas turbine engine
blade 10 having an under platform exterior surface. As described
further above, the metal substrate 40 of the gas turbine engine
blade 10 can comprise any of a variety of metals, or more typically
metal alloys, including those based on nickel, cobalt and/or iron
alloys. The substrate 40 may also be an aluminide bond coat as
known in the art.
[0057] The next step 205 is the masking of a preselected portion of
the turbine blade 10, wherein the portion masked is the portion of
the blade 10 that would not benefit from the roughening and
application of the corrosion resistant coating. The next step 210
is roughening the under platform surface 42 to make the surface 42
more receptive to the application of the coating of the present
invention. As described above, such roughening includes chemical
and/or mechanic pretreatment. Typically, the surface 42 of metal
substrate 40 is pretreated by grit blasting where surface 42 is
subjected to the abrasive action of silicon carbide particles,
steel particles, alumina particles or other types of abrasive
particles. These particles used in grit blasting are typically
alumina particles and typically have a particle size of from about
600 to about 35 mesh (from about 25 to about 500 micrometers), more
typically from about 360 to about 35 mesh (from about 35 to about
500 micrometers).
[0058] The next step 215 is depositing a first layer of corrosion
resistant coating composition on the surface 42 of the metal
substrate 40. As set forth above, the corrosion resistant coating
composition is disclosed in U.S. patent application Ser. No.
11/011,695, filed Dec. 15, 2004, entitled "CORROSION RESISTANT
COATING COMPOSITION, COATED TURBINE COMPONENT AND METHOD FOR
COATING SAME", which is incorporated by reference herein in its
entirety. The corrosion resistant coating composition can be
deposited in solid form, e.g., as a flowable solid, as a cast tape
(e.g., a cast tape formed as a layer or plurality layers of
particulates adhered together as a coherent mass or matrix by the
binder, with or without a supporting structure such as a film,
strip, etc.), etc., to provide a solid uncured layer of the
composition comprising the corrosion resistant particulates and
binder component. More typically, the coating composition is
deposited as a liquid, e.g., an aqueous coating composition. Liquid
corrosion resistant coating compositions of this invention can be
deposited on substrate 40 by any manner of application for
depositing liquids including pouring, flowing, dipping, spraying,
rolling, etc., to provide an uncured layer of the composition
comprising the particulates and binder component. In a preferred
embodiment, the non-alumina corrosion resistant particulates are
selected from the group consisting of an overlay metal alloy,
zirconia, yttria-stabilized zirconia, and combinations thereof. In
a more preferred embodiment, the non-alumina corrosion resistant
particulates are selected from the group consisting of NiCaAlY,
CoCrAlY, zirconia, yttria-stabilized zirconia, and combinations
thereof.
[0059] The next step 220 is curing the first deposited coating at a
temperature that causes the corrosion resistant particulate
component (i.e., non-alumina particulates, plus any alumina
particulates) and glass-forming binder component to form an inner
layer of the corrosion resistant coating 64 adjacent to metal
substrate 40 that comprises an amorphous, glassy matrix of binder
to which the particulates in the particulate component are embedded
in, encapsulated in, enclosed by, or otherwise adhered to. This
curing is typically accomplished by heating to a temperature of at
least about 250.degree. F. (121.degree. C.), more typically at
least about 500.degree. F. (260.degree. C.) to form the inner layer
64 of corrosion resistant coating. If any liquid carrier component
is present in the first deposited coating, the liquid carrier
component is evaporated and/or vaporized during the step of curing
220.
[0060] The next step 225 is depositing an additional layer of
corrosion resistant coating composition of this invention or from
other coating compositions. At least the inner layer 64 adjacent to
metal substrate 40 is formed from the corrosion resistant coating
composition of this invention. As described above, the corrosion
resistant coating composition or other coating compound can be
deposited in solid form, e.g., as a flowable solid, as a cast tape
(e.g., a cast tape formed as a layer or plurality layers of
particulates adhered together as a coherent mass or matrix by the
binder, with or without a supporting structure such as a film,
strip, etc.), etc., to provide a solid uncured layer of the
composition comprising the particulates and binder component.
[0061] The next step 230 is curing the additionally deposited
coating composition at a temperature that causes the additionally
deposited composition to form an inner layer of the corrosion
resistant coating 62 adjacent to metal substrate 40. This curing is
typically accomplished by heating to a temperature of at least
about 250.degree. F. (121.degree. C.), more typically at least
about 500.degree. F. (260.degree. C.) to form an additional layer
68 of corrosion resistant coating. If any liquid carrier component
is present in the additionally deposited coating, the liquid
carrier component is evaporated and/or vaporized during the step of
curing 230. Alternately, steps 225 and 230 may be repeated a
preselected number of times, with the corrosion resistant
particulate component or other being applied a preselected number
of times until the total coating thickness is a preselected
thickness.
[0062] As shown in FIG. 6, with one exemplary additional layer,
when no sealant layer is added to the surface 70 of the uppermost
layer 68, the surface 70 of the uppermost layer is the surface 32
of the under platform corrosion resistant coating, shown generally
as 62. The respective layers of coating 62 can have the same or
differing thicknesses. These layers typically tend to decrease in
thickness in the direction from the inner layers (i.e., those
closer to substrate 40) to the outer layers (i.e., those layers
further away from substrate 40). The coating composition used in
forming each of the respective layers can have the same or
differing levels of particulate component and glass-forming binder
component, as well as the same or differing types of particulates
in the particulate component.
[0063] The coating composition used in forming each of the
respective layers can also have the same or a differing binder
component, for example, magnesium phosphate in the inner layers and
aluminum phosphate in the outer layers. In addition, the level of
alumina particulates in the particulate component of the coating
composition can differ in the respective layers, and typically
increases from the inner layers to the outer layers. For example,
the inner layer or layers adjacent to the metal substrate can be
formed from the corrosion resistant coating compositions of this
invention comprising a level or amount of non-alumina particulates
(e.g., at least about 5%, typically at least about 25%, more
typically at least about 50% and potentially 100%) having a better
CTE match with the metal substrate, while the outer layer or layers
not adjacent to the metal substrate can comprise a level or amount
of alumina particulates (e.g., up to and including 100% alumina
particulates) so as not to be measurably different from the CTE of
alumina. Each layer of coating 62 deposited can be cured to the
same or different degrees.
[0064] The next optional step 235 is applying a layer of sealant
material to the surface of the cured corrosion resistant layer 54.
An embodiment of a corrosion resistant coating of this invention
comprising a plurality of coating layers 64, 66 and an outer
sealant layer 74 is shown in FIG. 7 generally as 72. This outer
sealant layer 74 can comprise a particulate component, but is
typically substantially free of particulates. Typically, outer
layer 74 is formed from a sealant composition or a composition that
consists essentially of, or entirely of, a glass-forming binder
component (i.e., is substantially free of particulates) to form a
glassy outer sealant layer. The next step 230 is curing the sealant
layer 56. This curing is typically accomplished by heating to a
temperature of at least about 250.degree. F. (121.degree. C.), more
typically at least about 500.degree. F. (260.degree. C.) to form
corrosion resistant coating 52. If any liquid carrier component is
present in the layer of sealant material, the liquid carrier
component is evaporated and/or vaporized during the step of curing
230. Outer layer 56 is also typically thinner than the underlying
layer 52, especially when substantially free of particulates. If
desired, an outer glassy sealant layer can be formed for coating 72
by depositing and curing a composition that is similar to or
consists essentially of a glass-forming binder component that is
substantially free of the particulate component, e.g., a sealant
composition. Such outer glassy sealant layers can be formed from
commercially available sealant products, for example, Alseal 598
(from Coatings for Industry, Inc. of Souderton, Pa.), SermaSeal TCS
(from Sermatech International of Pottstown, Pa.), etc.
[0065] As shown in FIG. 7, coating 72 comprises a first inner layer
64 that is adjacent to and overlaying metal substrate 60, and is
formed from a corrosion resistant coating composition of this
invention. In the embodiment shown, inner layer 64 is relatively
thick compared to any subsequent layers 68, 74 and preferably has a
thickness of from about 0.1 to about 5 mils (from about 3 to about
127 microns), more preferably from about 0.2 to about 4 mils (from
about 5 to about 102 microns). The particulate component comprising
inner layer 168 also typically has a greater level or amount of
non-alumina particulates, relative to the amount or level of
alumina particulates, to provide a better CTE match with substrate
60. The particulate component in inner layer 168 comprises from 0
to about 95% alumina particulates and from about 5 to 100%
non-alumina particulates, typically from 0 to about 75% alumina
particulates and from about 25 to 100% non-alumina particulates,
more typically from 0 to about 50% alumina particulates and from
about 50 to 100% non-alumina particulates, and can potentially
consist essentially of, or entirely of (i.e., is 100%), non-alumina
particulates.
[0066] Coating 72 also comprises an additional layer indicated
generally as 68 adjacent to and overlaying the surface 66 of inner
layer 64. Additional layer 68 is typically relatively thinner,
especially relative to inner layer 64. Additional layer 68
typically has thickness of from about 0.01 to about 5 mils (from
about 0.3 to about 127 microns), more typically from about 0.1 to
about 3 mils (from about 3 to about 76 microns). The particulate
component of additional layer 68 can also comprise an increased
amount or level of alumina particulates than that present in inner
layer 64 because there is less of a need for a CTE match with inner
layer 64. For example, additional layer 68 can potentially have a
CTE that is not measurably different from that of alumina.
Typically, the particulate component in additional layer 68 can
comprise from 0 to about 100% alumina particulates and from 0 to
100% non-alumina particulates, and can potentially consist
essentially of, or entirely of (i.e., is 100%), alumina
particulates.
[0067] As shown in FIG. 7, coating 72 can further comprise an outer
sealant layer indicated generally as 74 adjacent to and overlaying
the surface 70 of additional layer 68. This sealant layer 74 can
comprise a particulate component, but is typically substantially
free of particulates. Typically, sealant layer 74 is formed from a
sealant composition or a composition that consists essentially of,
or entirely of, a glass-forming binder component (i.e., is
substantially free of particulates) to form a glassy outer sealant
layer. Outer sealant layer 74 is also typically the thinnest layer
of coating 164, especially when substantially free of particulates.
Typically, outer sealant layer 74 has a thickness of from about
0.01 to about 2 mils (from about 0.3 to about 51 microns), more
typically from about 0.1 to about 1 mils (from about 3 to about 25
microns). The final step 245 is removing the maskant as known in
the art.
[0068] The corrosion resistant coatings of this invention can also
be applied during original manufacture of the gas turbine engine
blade (i.e., an OEM turbine blade), after the turbine blade has
been in operation for a period of time, after other coatings have
been removed from the turbine blade (e.g., a repair situation),
etc.
[0069] While the invention has been described with reference to a
preferred embodiment, it will be understood by those skilled in the
art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the invention. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this invention, but that the invention will include
all embodiments falling within the scope of the appended
claims.
* * * * *