U.S. patent application number 12/421149 was filed with the patent office on 2009-07-30 for turbine component other than airfoil having ceramic corrosion resistant coating and methods for making same.
This patent application is currently assigned to General Electric Company. Invention is credited to Brian Thomas Hazel, Bangalore Aswatha Nagaraj, Jeffrey Allan Pfaendtner.
Application Number | 20090191347 12/421149 |
Document ID | / |
Family ID | 36570571 |
Filed Date | 2009-07-30 |
United States Patent
Application |
20090191347 |
Kind Code |
A1 |
Nagaraj; Bangalore Aswatha ;
et al. |
July 30, 2009 |
TURBINE COMPONENT OTHER THAN AIRFOIL HAVING CERAMIC CORROSION
RESISTANT COATING AND METHODS FOR MAKING SAME
Abstract
An article comprising a turbine component other than an airfoil
having a metal substrate and a ceramic corrosion resistant coating
overlaying the metal substrate. This coating has a thickness up to
about 5 mils (127 microns) and comprises a ceramic metal oxide
selected from the group consisting of zirconia, hafnia and mixtures
thereof. This coating can be formed by a method comprising the
following steps: (a) providing a turbine component other than an
airfoil comprising the metal substrate; (b) providing a gel-forming
solution comprising a ceramic metal oxide precursor; (c) heating
the gel-forming solution to a first preselected temperature for a
first preselected time to form a gel; (d) depositing the gel on the
metal substrate; and (e) firing the gel at a second preselected
temperature above the first preselected temperature to form the
ceramic corrosion resistant coating comprising the ceramic metal
oxide. This coating can also be formed by alternative methods
wherein a ceramic composition comprising the ceramic metal oxide is
deposited by physical vapor deposition on the metal substrate to
provide a strain-tolerant columnar structure, or is thermal sprayed
on the metal substrate.
Inventors: |
Nagaraj; Bangalore Aswatha;
(West Chester, OH) ; Hazel; Brian Thomas; (West
Chester, OH) ; Pfaendtner; Jeffrey Allan; (Blue Ash,
OH) |
Correspondence
Address: |
HARTMAN AND HARTMAN, P.C.
552 EAST 700 NORTH
VALPARAISO
IN
46383
US
|
Assignee: |
General Electric Company
Schenectady
NY
|
Family ID: |
36570571 |
Appl. No.: |
12/421149 |
Filed: |
April 9, 2009 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11094351 |
Mar 31, 2005 |
|
|
|
12421149 |
|
|
|
|
Current U.S.
Class: |
427/376.2 |
Current CPC
Class: |
C23C 28/322 20130101;
F01D 5/288 20130101; F05D 2300/21 20130101; C23C 18/1254 20130101;
F01D 5/28 20130101; C23C 28/042 20130101; F05D 2300/611 20130101;
C23C 28/3455 20130101; C23C 30/00 20130101; C23C 28/345 20130101;
F01D 5/286 20130101; F05D 2260/95 20130101; C23C 18/1241 20130101;
C23C 18/1208 20130101; F05D 2300/2118 20130101; C23C 26/00
20130101; F05D 2230/90 20130101; F05D 2230/314 20130101; F01D
25/007 20130101; C23C 18/1283 20130101; C23C 18/1225 20130101; Y02T
50/60 20130101 |
Class at
Publication: |
427/376.2 |
International
Class: |
C04B 35/624 20060101
C04B035/624; B05D 3/00 20060101 B05D003/00 |
Claims
1. A method comprising the following steps: (a) providing a turbine
component other than a turbine airfoil comprising a metal
substrate; (b) providing a gel-forming solution comprising a
ceramic metal oxide precursor; (c) heating the gel-forming solution
to a first preselected temperature for a first preselected time to
form a gel; (d) depositing the gel on the metal substrate; and (e)
firing the deposited gel at a second preselected temperature above
the first preselected temperature to form a ceramic corrosion
resistant coating comprising a ceramic metal oxide, wherein the
ceramic metal oxide is selected from the group consisting of
zirconia, hafnia and mixtures thereof.
2. The method of claim 1 wherein step (d) is carried out by
applying at least one layer of the gel on the metal substrate.
3. The method of claim 2 wherein step (d) is carried out by
applying a plurality of layers of the gel on the metal
substrate.
4. The method of claim 1 wherein the gel-forming solution provided
in step (b) further comprises inert oxide filler particles.
5. The method of claim 1 wherein after step (e), the ceramic
corrosion resistant coating has a thickness of from about 0.01 to
about 1 mils.
6. The method of claim 1 wherein the turbine component provided
during step (a) is a compressor or turbine disk.
7. The method of claim 1 wherein the turbine component provided
during step (a) is a seal element.
Description
REFERENCE TO PREVIOUS APPLICATIONS
[0001] This application is a Division of co-pending U.S. patent
application Ser. No. 11/094,351 filed Mar. 31, 2005.
BACKGROUND OF THE INVENTION
[0002] This invention broadly relates to turbine components other
than airfoils, such as turbine disks, turbine seals and other
static components, having thereon a ceramic corrosion resistant
coating. This invention further broadly relates to methods for
forming such coatings on the turbine component.
[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 turbines 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. 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. As the maximum operating temperature of the turbine engine
increases, the turbine disks/shafts and seal elements are subjected
to higher temperatures. As a result, oxidation and corrosion of the
disks/shafts and seal elements 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, concrete dust, sand, sea salt, etc.,
are a major source of the corrosion, but other elements in the
aggressive bleed gas environment (e.g., air extracted from the
compressor to cool hotter components in the engine) can also
accelerate the corrosion. Alkaline sulfate corrosion in the
temperature range and atmospheric region of interest results in
pitting of the turbine disk/shaft and seal element substrate at
temperatures typically starting around 1200.degree. F. (649.degree.
C.). This pitting corrosion has been shown to occur on critical
turbine disk/shaft and seal elements. The oxidation and corrosion
damage can lead to premature removal and replacement of the
disks/shafts and seal elements unless the damage is reduced or
repaired.
[0006] Turbine disks/shafts and seal elements for use at the
highest operating temperatures are typically made of nickel-base
superalloys selected for good elevated temperature toughness and
fatigue resistance. These superalloys 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. Disks and other rotor components made from
newer generation alloys can also contain lower levels of aluminum
and/or chromium, and can therefore be more susceptible to corrosion
attack.
[0007] Corrosion resistant diffusion coatings can also be formed
from aluminum or chromium, or from the respective oxides (i.e.,
alumina or chromia). See, for example, commonly assigned U.S. Pat.
No. 5,368,888 (Rigney), issued Nov. 29, 1994 (aluminide diffusion
coating); and 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 considered for use on
turbine disk/shaft and seal elements. See, for example, U.S. Patent
Application No. 2004/0013802 (Ackerman et al), published Jan. 22,
2004, which discloses metal-organic chemical vapor deposition
(MOCVD) of aluminum, silicon, tantalum, titanium or chromium oxide
on turbine disks and seal elements to provide a protective coating.
These prior corrosion resistant coatings can have a number of
disadvantages, including: (1) possibly adversely affecting the
fatigue life of the turbine disks/shafts and seal elements because
these prior coatings diffuse into the underlying metal substrate;
(2) coefficient of thermal expansion (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
depositing the corrosion resistant coating on the metal
substrate.
[0008] Accordingly, there is still a need for coatings for turbine
disks, turbine shafts, turbine seal elements and other non-airfoil
turbine components that: (1) provide corrosion resistance,
especially at higher or elevated temperatures; (2) without
affecting other mechanical properties of the underlying metal
substrate or potentially causing other undesired effects such as
spalling; and (3) can be formed by relatively uncomplicated and
inexpensive methods.
BRIEF DESCRIPTION OF THE INVENTION
[0009] An embodiment of this invention broadly relates to an
article comprising a turbine component other than an airfoil having
a metal substrate and a ceramic corrosion resistant coating
overlaying the metal substrate, wherein the ceramic corrosion
resistant coating has a thickness up to about 5 mils (127 microns)
and comprises a ceramic metal oxide selected from the group
consisting of zirconia, hafnia and mixtures thereof.
[0010] Another embodiment of this invention broadly relates to a
method for forming this ceramic corrosion resistant coating on the
underlying metal substrate of the turbine component. One embodiment
of this method comprises the following steps:
[0011] (a) providing a turbine component other than an airfoil
comprising a metal substrate;
[0012] (b) providing a gel-forming solution comprising a ceramic
metal oxide precursor;
[0013] (c) heating the gel-forming solution to a first preselected
temperature for a first preselected time to form a gel;
[0014] (d) depositing the gel on the metal substrate; and
[0015] (e) firing the deposited gel at a second preselected
temperature above the first preselected temperature to form a
ceramic corrosion resistant coating comprising a ceramic metal
oxide, wherein the ceramic metal oxide is selected from the group
consisting of zirconia, hafnia and mixtures thereof.
[0016] An alternative embodiment of this method for forming this
coating comprises the following steps:
[0017] (a) providing a turbine component other than an airfoil
comprising a metal substrate; and
[0018] (b) depositing a ceramic composition comprising a ceramic
metal oxide on the metal substrate by physical vapor deposition to
form a ceramic corrosion resistant coating comprising the ceramic
metal oxide and having a strain-tolerant columnar structure,
wherein the ceramic metal oxide is selected from the group
consisting of zirconia, hafnia and mixtures thereof.
[0019] Another alternative embodiment of this method for forming
this coating comprises the following steps:
[0020] (a) providing a turbine component other than an airfoil
comprising a metal substrate; and
[0021] (b) thermal spraying a ceramIC composition comprising a
ceramic metal oxide on the metal substrate to form the ceramic
corrosion resistant coating comprising the ceramic metal oxide,
wherein the ceramic metal oxide is selected from the group
consisting of zirconia, hafnia and mixtures thereof.
[0022] The ceramic corrosion resistant coating of this invention
provides a number of significant benefits and advantages. Because
the ceramic corrosion resistant coating comprises a zirconia and/or
hafnia as the ceramic metal oxide, it does not diffuse into the
underlying metal substrate. As a result, the ceramic corrosion
resistant coating does not adversely affect the fatigue properties
of the coated turbine disk/shafts, seal elements and other turbine
components.
[0023] Because of the greater coefficient of thermal expansion
match between the ceramic metal oxide and the underlying metal
substrate, the ceramic corrosion resistant coating of this
invention provides greater adherence to the substrate and thus
greater resistance to spalling. This increased adherence will also
further improve the fatigue properties of the coated turbine
disks/shafts, seal elements and other turbine components by
resisting propagation ofcracks though the thickness of the coating
into the metal substrate.
[0024] These ceramic corrosion resistant coating can be formed by
embodiments of the method of this invention that are relatively
uncomplicated and inexpensive. In addition, the ceramic corrosion
resistant coating can be formed by embodiments of the methods of
this invention as a relatively thin layer on the metal
substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a schematic sectional view of a portion of the
turbine section of a gas turbine engine.
[0026] FIG. 2 is a sectional view of an embodiment of the ceramic
corrosion resistant coating of this invention deposited on the
metal substrate of a turbine rotor component.
[0027] FIG. 3 is a frontal view of a turbine disk showing where the
ceramic corrosion resistant coating of this invention is desirably
located.
DETAILED DESCRIPTION OF THE INVENTION
[0028] As used herein, the term "ceramic metal oxide" refers to
zirconia, hafnia or combinations of zirconia and hafnia (i.e.,
mixtures thereof). These ceramic metal oxides were previously used
in thermal barrier coatings that are capable of reducing heat flow
to the underlying metal substrate of the article, i.e., forming a
thermal barrier, and which have a melting point that is typically
at least about 2600.degree. F. (1426.degree. C.), and more
typically in the range of from about from about 3450.degree. to
about 4980.degree. F. (from about 1900.degree. to about
2750.degree. C.). The ceramic metal oxide can comprise 100 mole %
zirconia, 100 mole % hafnia, or any percentage combination of
zirconia and hafnia that is desired. Typically, the ceramic metal
oxide comprises from about 85 to 100 mole % zirconia and from 0 to
about 15 mole % hafnia, more typically from about 95 to 100 mole %
zirconia and from 0 to about 5 mole % hafnia.
[0029] As used herein, the term "ceramic metal oxide precursor"
refers to any composition, compound, molecule, etc., that is
converted into or forms the ceramic metal oxide, for example, from
the respective ceramic metal hydroxide, at any point up to and
including the formation of the ceramic corrosion resistant
coating.
[0030] As used herein, the term "ceramic corrosion resistant
coating" refers to coatings of this invention that 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, concrete dust, sand, sea salt, etc.;
at temperatures typically of at least about 10000 p (538.degree.
C.), more typically at least about 12000 p (649.degree. C.), and
which comprise the ceramic metal oxide. The ceramic corrosion
resistant coatings of this invention usually comprise at least
about 60 mole % ceramic metal oxide, typically from about 60 to
about 98 mole % ceramic metal oxide, and more typically from about
94 to about 97 mole % ceramic metal oxide. The ceramic corrosion
resistant coatings of this invention further typically comprise a
stabilizing amount of a stabilizer metal oxide for the ceramic
metal oxide. These stabilizer metal oxides can be selected from the
group consisting of yttria, calcia, scandia, magnesia, india,
gadolinia, neodymia, samaria, dysprosia, erbia, ytterbia, europia,
praseodymia, lanthana, tantala, etc., and mixtures thereof. The
particular amount of this stabilizer metal oxide that is
"stabilizing" will depend on a variety of factors, including the
stabilizer metal oxide used, the ceramic metal oxide used, etc.
Typically, the stabilizer metal oxide comprises from about 2 about
40 mole %, more typically from about 3 to about 6 mole %, of the
ceramic corrosion resistant coating. The ceramic corrosion
resistant coatings used herein typically comprise yttria as the
stabilizer metal oxide. See, for example, Kirk-Othmer's
Encyclopedia of Chemical Technology, 3rd Ed., Vol. 24, pp. 882-883
(1984) for a description of suitable yttria-stabilized
zirconia-containing ceramic compositions that can be used in the
ceramic corrosion resistant coatings of this invention.
[0031] As used herein, the term "ceramic composition" refers to
compositions used to form the ceramic corrosion resistant coatings
of this invention, and which comprise the ceramic metal oxide,
optionally but typically the stabilizer metal oxide, etc.
[0032] As used herein, the term "turbine component other than an
airfoil" refers to those turbine components that are not airfoils
(e.g., blades, vanes, etc.) that are formed from metals or metal
alloys, and include turbine disks (also referred to sometimes as
"turbine rotors"), turbine shafts, turbine seal elements that are
either rotating or static, including forward, interstage and aft
turbine seals, turbine blade retainers, other static turbine
components, etc. The turbine component for which the ceramic
corrosion resistant coatings of this invention are particularly
advantageous are those that experience a service operating
temperature of at least about 10000 p (538.degree. C.), more
typically at least about 12000 p (649.degree. C.), and typically in
the range of from about 1000.degree. to about 1600.degree. F. (from
about 538.degree. to about 871.degree. C.). These components are
usually exposed to turbine bleed air (e.g., air extracted from the
compressor to cool hotter components in the engine) having ingested
corrosive components, typically metal sulfates, sulfites,
chlorides, carbonates, etc., that can deposit on the surface of the
component. The ceramic corrosion resistant coatings of this
invention are particularly useful when formed on all or selected
portions of the surfaces of the component, such as the surfaces of
turbine disks/shafts and turbine seal elements. For example, the
mid-to-outer portion of the hub of a turbine disk can have the
ceramic corrosion resistant coating of this invention, while the
bore region, inner portion of the hub, and blade slots mayor may
not have this coating. In addition, the contact points or mating
surfaces between these components such as the disk post pressure
faces (i.e., the mating surface between the disk post and the
turbine blade dovetail), as well as the contact points between the
disks and seals, can be void or absent of the ceramic corrosion
resistant coating so as to retain desired or specified as produced
dimensions.
[0033] As used herein, the term "comprising" means various
coatings, compositions, metal oxides, 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."
[0034] All amounts, parts, ratios and percentages used herein are
by mole % unless otherwise specified.
[0035] The various embodiments of the turbine components having the
ceramic corrosion resistant coating of this invention are further
illustrated by reference to the drawings as described hereafter.
Referring to FIG. 1, a turbine engine rotor component 30 is
provided that can be of any operable type, for example, a turbine
disk 32 or a turbine seal element 34. FIG. 1 schematically
illustrates a stage 1 turbine disk 36, a stage 1 turbine blade 38
mounted to the turbine disk 36, a stage 2 turbine disk 40, a stage
2 turbine blade 42 mounted to the turbine disk 40, a forward
turbine seal 44 that also functions as a forward blade retainer for
blade 38, an aft turbine seal 46, and an interstage turbine seal 48
that also functions as a forward blade retainer for blade 42, an
aft blade retainer 50 for blade 38 that is held in place by seal
48, and an aft blade retainer 52 for blade 42. Any or all of these
turbine disks 32 (e.g., stage 1 turbine disk 36 and a stage 2
turbine disk 40), turbine seal elements 34 (e.g., forward turbine
seal 44, aft turbine seal 46, and interstage turbine seal 48)
and/or blade retainers 50/52, or any selected portion thereof, can
be provided with the ceramic corrosion resistant coating of this
invention, depending upon whether corrosion is expected or
observed.
[0036] Referring to FIG. 2, the metal substrate 60 of the turbine
engine rotor component 30 can comprise any of a variety of metals,
or more typically metal alloys, including those based on nickel,
cobalt and/or iron alloys. Substrate 60 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. 4,957,567 (Krueger et al), issued Sep. 18,
1990, and U.S. Pat. No. 6,521,175 (Mourer et al), issued Feb. 18,
2003, the relevant portions of which are incorporated by reference.
Superalloys are also generally described in Kirk-Othmer's
Encyclopedia of Chemical Technology, 3rd Ed., Vol. 12, pp. 417-479
(1980), and Vol. 15, pp. 787-800 (1981). Illustrative nickel-based
superalloys are designated by the trade names Inconel.RTM.,
Nimonic.RTM., Rene.RTM. (e.g., Rene.RTM. 88, Rene.RTM. 104, Rene N5
alloys), and Udime.RTM..
[0037] Substrate 60 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 ceramic corrosion
resistant coating of this invention is particularly useful is
available by the trade name Rene 88, which has a nominal
composition, by weight of 13% cobalt, 16% chromium, 4% molybdenum,
3.7% titanium, 2.1% aluminum, 4% tungsten, 0.70% niobium, 0.015%
boron, 0.03% zirconium, and 0.03 percent carbon, with the balance
nickel and minor impurities.
[0038] In forming the ceramic corrosion resistant coating 64 of
this invention on the surface 62 of metal substrate 60, surface 62
is typically pretreated mechanically, chemically or both to make
the surface more receptive for coating 64. 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 Niagara et al, issued Mar. 3, 1998, especially col. 4,
lines 46-66, which is incorporated by reference), 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), 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 incorporated by reference),
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 62 of metal
substrate 60 is pretreated by grit blasting where surface 62 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 400 to about 300 mesh (from about 38 to about
50 micrometers).
[0039] An embodiment of the method of this invention for forming
ceramic corrosion resistant coating 64 on metal substrate 60 is by
use of a sol-gel process. See commonly assigned U.S. Patent
Application No. 2004/0081767 (Pfaendtner et al), published Apr. 29,
2004, which is incorporated by reference. Sol-gel processing is a
chemical solution method to produce a ceramic oxide (e.g.,
zirconia). A chemical gel-forming solution which typically
comprises an alkoxide precursor or a metal salt is combined with
ceramic metal oxide precursor materials, as well as any stabilizer
metal oxide precursor materials, etc. A gel is formed as the
gel-forming solution is heated to slightly dry it at a first
preselected temperature for a first preselected time. The gel is
then applied over the surface 62 of metal substrate 60. Proper
application of the ceramic metal oxide precursor materials and
proper drying produce a continuous film over the surface 62. The
sol-gel can be applied to surface 62 of substrate 60 by any
convenient technique. For example, the sol-gel can be applied by
spraying at least one thin layer, e.g., a single thin layer, or
more typically a plurality of thin layers to build up a film to the
desired thickness for coating 64. The gel is then fired at a second
elevated preselected temperature above the first elevated
temperature for a second preselected time to form coating 64. The
ceramic corrosion resistant coating 64 comprises a dense matrix
that has a thickness of up to about 5 mils (127 microns) and
typically from about 0.01 to about 1 mils (from about 0.2 to about
25 microns), more typically from about 0.04 to about 0.5 mils (from
about 1 to about 13 microns). Optionally, inert oxide filler
particles can be added to the sol-gel solution to enable a greater
per-layer thickness to be applied to the substrate.
[0040] An alternative method for forming ceramic corrosion
resistant coating 64 is by physical vapor deposition (PVD), such as
electron beam PVD (EB-PVD), filtered arc deposition, or by
sputtering. Suitable sputtering techniques for use herein include
but are not limited to direct current diode sputtering, radio
frequency sputtering, ion beam sputtering, reactive sputtering,
magnetron sputtering and steered arc sputtering. PVD techniques can
form ceramic corrosion resistant coatings 64 having strain
resistant or tolerant microstructures such as vertical microcracked
structures. EB-PVD techniques can form columnar structures that are
highly strain resistant to further increase the coating adherence.
Although these strain resistant or tolerant structures have direct
paths between the coating surface 66 and the substrate 60, the
paths are sufficiently narrow that the partially molten or highly
viscous corrodant salts do not infiltrate or minimally infiltrate
the cracks of the vertically microcracked structures or column gaps
of the columnar structures.
[0041] Other suitable alternative methods for forming these ceramic
corrosion resistant coating include thermal spray, aerosol spray,
chemical vapor deposition (CVD) and pack cementation. As used
herein, the term "thermal spray" refers to any method for spraying,
applying or otherwise depositing the ceramic composition that
involves heating and typically at least partial or complete thermal
melting of the overlay coating material and depositing of the
heated/melted material, typically by entrainment in a heated gas
stream, onto the metal substrate to be coated. Suitable thermal
spray deposition techniques include plasma spray, such as air
plasma spray (APS) and vacuum plasma spray (YPS), high velocity
oxy-fuel (HYOF) spray, detonation spray, wire spray, etc., as well
as combinations of these techniques. A particularly suitable
thermal spray deposition technique for use herein is plasma spray.
Suitable plasma spray techniques are well known to those skilled in
the art. See, for example, Kirk-Othmer Encyclopedia of Chemical
Technology, 3rd Ed., Vol. 15, page 255, and references noted
therein, as well as U.S. Pat. No. 5,332,598 (Kawasaki et al),
issued Jul. 26, 1994; U.S. Pat. No. 5,047,612 (Savkar et al) issued
Sep. 10, 1991; and U.S. Pat. No. 4,741,286 (Hoh et al), issued May
3, 1998 (herein incorporated by reference) which are instructive in
regard to various aspects of plasma spraying suitable for use
herein.
[0042] Suitable methods for carrying out chemical vapor deposition
and/or pack cementation are disclosed in, for example, commonly
assigned U.S. Pat. No. 3,540,878 (Levine et al), issued Nov. 17,
1970; commonly assigned U.S. Pat. No. 3,598,638 (Levine), issued
Aug. 10, 1971; commonly assigned U.S. Pat. No. 3,667,985 (Levine et
al), issued Jun. 6, 1972, the relevant disclosures of which are
incorporated by reference. Metal-organic chemical vapor phase
deposition (MOCYD) processes can also be used herein. See commonly
assigned U.S. Patent Application No. 2004/0013802 (Ackerman et al),
published Jan. 22, 2004, the relevant disclosures of which are
incorporated by reference.
[0043] As illustrated in FIG. 3, typically only a portion of the
surface of these turbine disks/shafts, seals and/or blade retainers
are provided with the ceramic corrosion resistant coating 64 of
this invention. FIG. 3 shows a turbine disk 32 having an inner
generally circular hub portion indicated as 74 and an outer
generally circular perimeter or diameter indicated as 78, and a
periphery indicated as 82 that is provided with a plurality of
circumferentially spaced slots indicated as 86 for receiving the
root portion of turbine blades such as 38, 42. While the ceramic
corrosion resistant coating 64 can be applied to the entire surface
of disk 70, it is typically needed only on the surface of outer
diameter 78.
[0044] While the above embodiments have been described in the
context of coating turbine engine disks, this invention can be used
to form a ceramic corrosion resistant coating 64, as described
above, on the surfaces of various turbine engine rotor components,
including compressor disks, seals, and shafts, which can then be
exposed to corrosive elements at elevated temperatures. The ceramic
corrosion resistant coatings of this invention can also be applied
during original manufacture of the component (i.e., an OEM
component), after the component has been in operation for a period
of time, after other coatings have been removed from the component
(e.g., a repair situation), while the component is assembled or
after the component is disassembled, etc.
[0045] The following example illustrates an embodiment for forming
the ceramic corrosion coating of this invention on a metal
substrate by sol-gel processing and the benefits obtained
thereby:
[0046] A one inch round sample of Rene N5 alloy is coated with an
approximately 5 micron layer of a 7 wt. % yttria stabilized
zirconia deposited from a sol gel. A sulfate containing corrodant
is applied to the surface of the coating and run through a 2 hour
cycle at 1300.degree. F. (704.degree. C.). The first hour of the 2
hour cycle uses a reducing atmosphere to try to cause a reaction
between the corrodant and the surface of the coated sample, while
the second hour uses air to cause corrosion scale growth. The
corrodant is removed by water washing and coated sample is then
inspected for damage. This corrosion application, thermal exposure,
cleaning and inspection cycle is repeated until the coated sample
shows signs of damage. After 8 cycles no appreciable damage is
noted on the coated sample. After 10 cycles, the coating is still
adherent to the a Hoy, but discoloration is noted and the coated
sample is cross-sectioned for evaluation. After cross-sectioning, a
corrosion production layer approximately 10 microns thick is found
below the coating. For comparison, this is representative of a bare
alloy sample (i.e., with no coating) after approximately 2 cycles
of such testing.
[0047] While specific embodiments of this invention have been
described, it will be apparent to those skilled in the art that
various modifications thereto can be made without departing from
the spirit and scope of this invention as defined in the appended
claims.
* * * * *