U.S. patent application number 11/109160 was filed with the patent office on 2006-03-16 for article having a surface protected by a silicon-containing diffusion coating.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. Invention is credited to Nrinpendra Nath Das, Jackie Lee King, Bangalore Aswatha Nagaraj, Matthew David Saylor.
Application Number | 20060057416 11/109160 |
Document ID | / |
Family ID | 32506456 |
Filed Date | 2006-03-16 |
United States Patent
Application |
20060057416 |
Kind Code |
A1 |
Das; Nrinpendra Nath ; et
al. |
March 16, 2006 |
Article having a surface protected by a silicon-containing
diffusion coating
Abstract
A surface of an article is protected by coating the surface with
a silicon-containing coating by preparing a coating mixture of
silicon, a halide activator, and an oxide powder, positioning the
surface of the article in gaseous communication with the coating
mixture, and heating the surface of the article and the coating
mixture to a coating temperature of from about 1150.degree. F. to
about 1500.degree. F. The article is preferably a component of a
gas turbine engine made of a nickel-base superalloy.
Inventors: |
Das; Nrinpendra Nath; (West
Chester, OH) ; Nagaraj; Bangalore Aswatha; (West
Chester, OH) ; Saylor; Matthew David; (Blanchester,
OH) ; King; Jackie Lee; (Franklin, OH) |
Correspondence
Address: |
MCNEES, WALLACE & NURICK LLC
100 PINE STREET
PO BOX 1166
HARRISBURG
PA
17108-1166
US
|
Assignee: |
GENERAL ELECTRIC COMPANY
Schenectady
NY
|
Family ID: |
32506456 |
Appl. No.: |
11/109160 |
Filed: |
April 19, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10318762 |
Dec 13, 2002 |
6933012 |
|
|
11109160 |
Apr 19, 2005 |
|
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Current U.S.
Class: |
428/610 |
Current CPC
Class: |
C23C 10/08 20130101;
Y10T 428/12674 20150115; Y10T 428/12458 20150115; C23C 10/46
20130101 |
Class at
Publication: |
428/610 |
International
Class: |
B22D 25/00 20060101
B22D025/00 |
Claims
1-17. (canceled)
18. An article comprising a component of a gas turbine engine
having a nickel-base superalloy substrate composition; and a
protective layer at a surface of the component, wherein the
protective layer comprises a mixture of silicon and elements from
the substrate composition interdiffused with the silicon.
19. The article of claim 18, wherein the substrate has a nominal
composition, in weight percent, of 13 percent cobalt, 10 percent
chromium, 4 percent molybdenum, 3.7 percent titanium, 2.1 percent
aluminum, 4 percent tungsten. 0.75 percent niobium, 0.015 percent
boron, 0.03 percent zirconium, and 0.03 percent carbon, up to about
0.5 percent iron, balance nickel arid minor amounts of other
elements; or has a nominal composition, in weight percent, of about
20.6 percent cobalt, about 13.0 percent chromium, about 3.4 percent
aluminum, about 3.7 percent titanium, about 2.4 percent tantalum,
about 0.90 percent niobium, about 2.10 percent tungsten, about 3.80
percent molybdenum, about 0.05 percent carbon, about 0.025 percent
boron, about 0.05 percent zirconium, up to about 0.5 percent iron,
balance nickel and minor amounts of other elements.
20. The article of claim 18, wherein the protective layer consists
essentially of a mixture of silicon and elements from the substrate
composition interdiffused with the silicon.
21. (canceled)
22. The article of claim 18, wherein the component is in a
cast-and-worked form.
23. The article of claim 18, wherein tile surface of the substrate
component is mechanically worked.
24. (canceled)
25. The article of claim 18, wherein the article is a turbine disk,
a seal, or a compressor component.
26. An article comprising a component of a gas turbine engine
having a nickel-base superalloy substrate composition In a
cast-and-worked form; and a protective layer at a surface of the
component, wherein the protective layer comprises silicon.
27. The article of claim 26, wherein the substrate has a nominal
composition, in weight percent, of 13 percent cobalt, 16 percent
chromium, 4 percent molybdenum, 3.7 percent titanium, 2.1 percent
aluminum, 4 percent tungsten, 0.75 percent niobium, 0.015 percent
boron, 0.03 percent zirconium, and 0.03 percent carbon, up to about
0.5 percent iron, balance nickel and minor amounts of other
elements; or has a nominal composition, in weight percent, of about
20.6 percent cobalt, about 13.0 percent chromium, about 3.4 percent
aluminum, about 3.7 percent titanium, about 2.4 percent tantalum,
about 0.90 percent niobium, about 2.10 percent tungsten, about 3.80
percent molybdenum, about 0.05 percent carbon, about 0.025 percent
boron, about 0.05 percent zirconium, up to about 0.5 percent iron,
balance nickel and minor amounts of other elements.
28. The article of claim 26, wherein the protective layer comprises
a mixture of silicon and elements from the substrate composition
interdiffused with the silicon.
29. (canceled)
30. The article of claim 18, wherein the protective layer is
substantially pure silicon at the surface of the component.
31. The article of claim 26, wherein the protective layer is
substantially pure silicon at the surface of the component.
32. An article comprising a component having a nickel-base
superalloy substrate composition; and a protective layer at a
surface of the component, wherein the protective layer comprises a
mixture of silicon and elements from the substrate composition
interdiffused with the silicon, and wherein the protective layer
has a gradient composition with a greatest percentage of silicon at
the surface of the component and a reduced percentage of silicon
with increasing distance into the component from the surface of the
component.
33. The article of claim 32, wherein the substrate has a nominal
composition, in weight percent, of 13 percent cobalt, 16 percent
chromium, 4 percent molybdenum, 3.7 percent titanium, 2.1 percent
aluminum, 4 percent tungsten, 0.75 percent niobium, 0.015 percent
boron, 0.03 percent zirconium, and 0.03 percent carbon, up to about
0.5 percent iron, balance nickel and minor amounts of other
elements; or has a nominal composition, in weight percent, of about
20.6 percent cobalt, about 13.0 percent chromium, about 3.4 percent
aluminum, about 3.7 percent titanium, about 2.4 percent tantalum,
about 0.90 percent niobium, about 2.10 percent tungsten, about 3.80
percent molybdenum, about 0.05 percent carbon, about 0.025 percent
boron, about 0.05 percent zirconium, up to about 0.5 percent iron,
balance nickel and minor amounts of other elements.
34. The article of claim 32, wherein the protective layer consists
essentially of a mixture of silicon and elements from the substrate
composition interdiffused with the silicon.
35. The article of claim 32, wherein the component is in a
cast-and-worked form.
36. The article of claim 32, wherein the surface of the component
is mechanically worked.
37. The article of claim 32, wherein the article is a turbine disk,
a seal, or a compressor component.
38. The article of claim 32, wherein the protective layer is
substantially pure silicon at the surface of the component.
Description
[0001] This invention relates to the protection of a surface with a
coating, and more particularly to the protection of a nickel-base
superalloy gas turbine component with a silicon-containing
coating.
BACKGROUND OF THE INVENTION
[0002] In a basic form of an aircraft gas turbine (jet) 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 combustion gas is passed through a turbine
mounted on the same shaft. The turbine includes a turbine disk
(sometimes termed the "rotor"), upon which turbine blades are
mounded. The flow of combustion gas turns the turbine by
impingement against an airfoil section of the turbine blades, which
turns the shaft and provides power to the compressor. Seals prevent
the leakage of hot combustion gas around the turbine. After passing
through the turbine, the hot combustion gas flows from the back of
the engine, driving it and the aircraft forward.
[0003] In prior generations of aircraft gas turbine engines, the
turbine disks and seal components operated at a sufficiently low
temperature that hot corrosion was not a major concern. In current
and advanced gas turbine engines, however, some of the components,
such as the turbine disk and some of the seal components, are
operated at a sufficiently high temperature that they are subjected
to hot corrosion during operation. The corrodant is introduced into
the turbine section of the engine in the hot combustion gases. The
corrodant typically includes alkaline sulfate deposits that may
have carbon as well.
[0004] Nickel-base superalloys are used as the materials of
construction of some types of turbine disks and seal components. In
service, the nickel-base superalloys are exposed to hot corrosion
in the intermediate temperature range of about 1000.degree. F. to
about 1500.degree. F. The compositions of the nickel-base
superalloys are selected to achieve the required mechanical
properties in service. However, the superalloys that have the
desired mechanical properties are not sufficiently resistant to
hot-corrosion damage. The hot-corrosion damage, if it becomes
sufficiently severe, may cause the superalloy component to fail
prematurely.
[0005] Environmentally resistant coatings are known for use with
nickel-base superalloys operated at higher temperatures.
Aluminum-containing diffusional and overlay coatings that oxidize
to produce a protective aluminum oxide scale are widely used.
However, these coatings are typically not suitable for use on
wrought gas turbine components operated in the temperature range of
about 1000.degree. F. to about 1500.degree. F., because they
require higher deposition temperatures that adversely affect the
mechanical properties of the heat-treated wrought nickel-base
superalloys.
[0006] There is a need for an improved approach to the protection
of nickel-base superalloys and other materials operated in a
corrosive environment in the temperature range of about
1000.degree. F. to about 1500.degree. F. The new approach must be
compatible with the processing of the component. The present
invention fulfills this need, and further provides related
advantages.
BRIEF SUMMARY OF THE INVENTION
[0007] The present approach provides a method for protecting a
surface of an article. It is particularly useful for protecting a
component of a gas turbine engine that is operated in a temperature
range of from about 1000.degree.20 F. to about 1500.degree. F. and
potentially subject to hot corrosion from the hot combustion gases,
such as gas turbine disks and some seal components. The present
approach protects the surface of the article, is compatible with
the thermomechanical processing of wrought nickel-base superalloys
used to manufacture the articles, and is compatible with achieving
and maintaining the mechanical properties required in the article.
The coating approach is not limited by line of sight access to the
surface that is to be protected. It is also environmentally
friendly and readily used in commercial operations.
[0008] A method for protecting a surface of an article comprises
the steps of providing the article having the surface thereon, and
thereafter coating the surface with a silicon-containing coating.
The coating is accomplished by preparing a coating mixture having
silicon, a halide activator, and an oxide powder, positioning the
surface of the article in gaseous communication with the coating
mixture, and heating the surface of the article and the coating
mixture to a coating temperature of from about 1150.degree. F. to
about 1500.degree. F., typically in an oven. Most preferably, the
surface is contacted to the coating mixture, as by packing the
coating mixture around and in contact with the surface.
[0009] The coating mixture preferably has from about 2 to about 10
percent by weight of silicon powder, from about 0.1 to about 0.5
percent by weight of a halide activator, and the balance aluminum
oxide powder. The coating is preferably performed in an inert
atmosphere or hydrogen. The heating time is determined by the
desired thickness of the protective layer, but is typically on the
order of from about 2 to about 8 hours.
[0010] The article is preferably made of a nickel-base superalloy,
and most preferably a wrought nickel-base superalloy. Examples of
such articles are components of a gas turbine engine, such as
turbine disks and seals. The surface of the article may be
mechanically worked before it is coated.
[0011] The resulting article is preferably a component of a gas
turbine engine having a nickel-base superalloy substrate
composition, with a protective layer at the surface of the
component. The protective layer comprises a mixture of silicon and
elements from the substrate composition interdiffused with the
silicon. Most preferably, the protective layer consists essentially
of a mixture of silicon and elements from the substrate composition
interdiffused with the silicon.
[0012] The protected article is preferably operated in a gas
turbine at an operating temperature of from about 1000.degree. F.
to about 1500.degree. F. and contacted by hot combustion gas.
[0013] When the coating mixture is heated during the coating step,
the chemical reaction between the silicon and the halide activator
produces a silicon-containing gas. An example is silicon fluoride
in the case of a fluoride-containing activator. The
silicon-containing gas is transported to the component, which
serves as a substrate for the deposition of the silicon-containing
gas. Upon contacting the surface of the substrate, the
silicon-containing gas decomposes to deposit silicon on the
substrate. Because the reaction and the vapor-phase transport are
performed at elevated temperatures, the silicon interdiffuses with
elements from the substrate composition to produce a silicon-rich
surface layer. The silicon-rich surface layer protects the article
against corrosion by the corrosive components of the hot combustion
gas.
[0014] The present protection approach, which does not require that
the component be heated during processing to a temperature above
its normal service operating temperature, is fully compatible with
the thermomechanical and other processing treatments of wrought
nickel-base superalloys that are used in the preferred components
such as gas turbine disks and seals. 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. The scope of the
invention is not, however, limited to this preferred
embodiment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a perspective view of a protected component of a
gas turbine engine;
[0016] FIG. 2 is a block flow diagram of an approach for protecting
the component;
[0017] FIG. 3 is a schematic sectional view of a coating apparatus
with the article packed in the coating mixture; and
[0018] FIG. 4 is a schematic sectional view of the protected
component of FIG. 1, taken on line 4-4.
DETAILED DESCRIPTION OF THE INVENTION
[0019] The present approach may be used to process a wide variety
of physical forms of workpieces to produce a wide variety of final
articles 20. Components of gas turbine engines are of particular
interest. FIG. 1 illustrates one such article 20, a turbine disk 22
having an article surface 24. Other components include, for
example, seals and compressor components. The present approach is
not limited to the production of these articles, however.
[0020] FIG. 2 depicts a preferred approach for protecting the
surface 24 of the article 20. The article 20 having the article
surface 24 thereon is provided, step 30. The article 20 is
furnished in substantially its final size and shape, and underlying
base-metal composition. The surface protection treatment to be
described subsequently alters the dimensions of the article only
very slightly.
[0021] The article 20 is preferably made of a nickel-base alloy as
the base metal, and is most preferably made of a nickel-base
superalloy. A nickel-base alloy is a composition of matter having
more nickel than any other element. A nickel-base superalloy is a
nickel-base alloy that is hardenable by the precipitation of gamma
prime or a related phase. A presently preferred nickel-base
superalloy that is to be protected by the present approach is
Rene.TM. 88DT, having a nominal composition, in weight percent, of
13 percent cobalt, 16 percent chromium, 4 percent molybdenum, 3.7
percent titanium, 2.1 percent aluminum, 4 percent tungsten, 0.75
percent niobium, 0.015 percent boron, 0.03 percent zirconium, and
0.03 percent carbon, up to about 0.5 percent iron, balance nickel
and minor amounts of other elements. Another example is alloy ME3,
having a nominal composition, in weight percent, of about 20.6
percent cobalt, about 13.0 percent chromium, about 3.4 percent
aluminum, about 3.7 percent titanium, about 2.4 percent tantalum,
about 0.90 percent niobium, about 2.10 percent tungsten, about 3.80
percent molybdenum, about 0.05 percent carbon, about 0.025 percent
boron, about 0.05 percent zirconium, up to about 0.5 percent iron,
balance nickel and minor amounts of other elements. These alloys
are presented by way of example, and the use of the present
invention is not so limited.
[0022] The nickel-base superalloy is desirably a wrought
nickel-base superalloy, which is cast and then mechanically worked,
usually by thermomechanical working at elevated temperature such as
by forging, to reach the shape of the article 20. It may also be
heat treated prior to working, at intermediate points in the
working process, and after working. The details of the working and
heat treating are known in the art for each alloy.
[0023] The surface 24 of the article 20 may be mechanically worked
or otherwise processed as a final stage of the providing step 30.
For example, the article surface 24 may be shot peened to induce a
desired stress state into the article surface 24. It may optionally
be grit blasted or vapor honed.
[0024] The working, heat treating, mechanical working, and other
processing produce a desired structure and stress state at the
surface 24 and in the microstructure of the article 20. This
structure and stress state may not be disturbed or altered by
heating the article 20 to a temperature of greater than about
1500.degree. F. in subsequent processing, or the mechanical
performance under service conditions of the article 20 will be
adversely affected.
[0025] The article surface 24 is thereafter coated with a
silicon-containing coating, step 32. The coating operation 32 first
includes preparing a coating mixture of silicon, a halide
activator, and an oxide powder, step 34. The silicon is preferably
furnished as silicon powder of any operable size, most preferably
-100 mesh. The halide activator is of any operable type. Operable
halide activators include, for example, ammonium fluoride, ammonium
chloride, sodium fluoride, sodium chloride, sodium bromide, sodium
iodide, potassium fluoride, potassium chloride, potassium bromide,
potassium iodide, aluminum fluoride, and aluminum chloride, or
mixtures thereof. Most preferably, the halide activator is an
ammonium halide or an aluminum halide. The oxide powder is inert in
the coating operation and serves to slow the coating process and
prevent agglomeration of the powders that would prevent access of
the coating vapor to the surface 24. The oxide powder is preferably
aluminum oxide (alumina, or Al.sub.2O.sub.3). Any operable oxide
powder size may be used, but a preferred size is -325 mesh.
[0026] A preferred composition of the coating mixture is from about
2 to about 10 percent by weight of silicon powder, from about 0.1
to about 0.5 percent by weight of a halide activator, and the
balance aluminum oxide powder.
[0027] The surface 24 of the article 20 is positioned in gaseous
communication with the coating mixture, step 36. Any operable
approach may be used, but the presently preferred approach,
illustrated in FIG. 3, is to pack the coating mixture 50 in contact
with the surface 24 of the article, as by packing the entire
article 20 in the coating mixture 50. For example and as
illustrated, the article 20 may be placed into a container 52, and
the solid coating mixture 50 is poured into the container 52 to
surround and immerse the article 20.
[0028] The surface 24 of the article 20 and the coating mixture 50
are thereafter heated to a coating temperature of from about
1150.degree. F. to about 1500.degree. F., step 38. If the coating
temperature is lower than about 1150.degree. F., the rate of
coating is too slow to be commercially feasible. If the coating
temperature is greater than about 1500.degree. F., the stress
state, structure, and/or microstructure of the underlying article
20 are adversely affected.
[0029] The preferred approach is to heat the surface 24 of the
article 20 and the coating mixture 50 in an oven 54, see FIG. 3.
The oven 54 may be of any operable type, but is represented as an
electrically heated oven with electrical heating coils 56. The
heating 38 is preferably performed in an inert-gas (e.g., argon) or
hydrogen-reducing atmosphere, supplied by a gas source 58.
[0030] The heating causes the halide activator to react with the
silicon to produce a gaseous form. For example, if the halide
activator is ammonium fluoride, the ammonium fluoride decomposes to
produce fluoride ions. The fluoride ions react with the silicon to
produce a silicon-bearing gas such as gaseous silicon fluoride
(SiF.sub.6 or a related form). The silicon-bearing gas diffuses to
the surface 24 of the article 20. Upon contacting the surface 24,
the silicon-bearing gas decomposes to deposit silicon upon the
surface 24.
[0031] The article 20 thereby serves as a substrate 60 for the
deposition of the silicon and thence the protective coating 62, as
shown in FIG. 4. The silicon is initially deposited in elemental
form. However, because the deposition is performed at elevated
temperature, the deposited silicon interdiffuses with the base
metal of the substrate composition, which is a nickel-base
superalloy in the preferred embodiment. The protective coating 62
is therefore a diffusion coating whose composition is a gradient
composition extending through the protective coating 62. At the
surface 24, the protective coating 62 has its greatest percentage
silicon content and lowest percentage content of base-metal
elements from the substrate 60. The portion of the protective
coating 62 at and nearest the surface 24 may be substantially
completely pure silicon, if the silicon deposition in step 38 is
continued for a sufficiently long time. With increasing distance
below the surface 24, the percentage of silicon in the coating is
reduced, and the percentage of the base-metal elements of the
substrate 60 increases until it reaches 100 percent at the greatest
depth 64 of the protective coating 62. Optionally but not
preferably at the present time, other elements may be co-deposited
with the silicon to become part of the protective coating 62.
[0032] The heating step 38 is continued for a time sufficient to
produce the protective coating 62 of a desired thickness. A
preferred coating temperature range of from about 1250.degree. F.
to about 1400.degree. F. for a time of from about 2 to about 8
hours has been found sufficient for most applications of interest.
For example, a heating step 38 of about 5 hours at a coating
temperature of about 1400.degree. F. produces a protective coating
62 about 0.0007 inch thick. The coating temperature may, however,
range as low as 1150.degree. F. and as high as 1500.degree. F., as
discussed earlier.
[0033] After the coating 32 is complete, the article 20 with the
protective coating 62 thereon is final processed, step 40. The
final processing may include, for example, thermal treatments,
final machining of uncoated portions, and cleaning.
[0034] The article 20 with the protective coating 62 in place is
operated in service, step 42. In the preferred application, the
article 20 is operated at an operating temperature of from about
1000.degree. F. to about 1500.degree. F. and contacted by hot
combustion gas for an extended period of time.
[0035] One of the advantages of the present approach is that, after
service, the protective coating 62 may be restored and rejuvenated
by recoating, step 44. During service, it is expected that some of
the protective coating 62 would be corroded or eroded away, or
otherwise lost. To some extent the as-deposited protective coating
62 is "self-healing", as any excess silicon in the protective
coating 62 may interdiffuse with the substrate 60 during service.
Eventually, however, the protective coating 62 becomes thinner and
in some places may be lost entirely. To perform the recoating, step
32 is repeated after the article 20 is cleaned, and all
service-produced residue removed. Step 40 may optionally be
repeated as necessary. The article 20 may then be returned to
service, step 42. Subsequent recoatings/rejuvenations are
permissible.
[0036] The present approach has been reduced to practice. Flat
panel specimens of Rene.TM. 88DT were coated by the preferred
approach discussed above. The coated flat panel specimens and
uncoated specimens of Rene.TM. 88DT were exposed at 1300.degree. F.
to a sodium sulfate corrodant mixture and periodically evaluated.
The coated specimens had about three times the life of the uncoated
specimens.
[0037] Although a particular embodiment of the invention has been
described in detail for purposes of illustration, various
modifications and enhancements may be made without departing from
the spirit and scope of the invention. Accordingly, the invention
is not to be limited except as by the appended claims.
* * * * *