U.S. patent application number 12/341855 was filed with the patent office on 2009-04-23 for titanium treatment to minimize fretting.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. Invention is credited to Robert William BRUCE.
Application Number | 20090104041 12/341855 |
Document ID | / |
Family ID | 37075910 |
Filed Date | 2009-04-23 |
United States Patent
Application |
20090104041 |
Kind Code |
A1 |
BRUCE; Robert William |
April 23, 2009 |
TITANIUM TREATMENT TO MINIMIZE FRETTING
Abstract
A method for surface treating a titanium gas turbine engine
component. The method includes providing a gas turbine engine
component having a titanium-containing surface. The component is
heated to a temperature sufficient to diffuse carbon into the
titanium and below 1000.degree. F. The surface is contacted with a
carbon-containing gas to diffuse carbon into the surface to form
carbides. Thereafter, the carbide-containing surface is coated with
a lubricant comprising a binder and a friction modifier. The binder
preferably including titanium oxide and the friction modifier
preferably including tungsten disulfide. The coefficient of
friction between the surface and another titanium-containing
surface is less than about 0.6 in high altitude atmospheres.
Inventors: |
BRUCE; Robert William;
(Loveland, 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: |
37075910 |
Appl. No.: |
12/341855 |
Filed: |
December 22, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11247686 |
Oct 11, 2005 |
|
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12341855 |
|
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60694759 |
Jun 28, 2005 |
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Current U.S.
Class: |
416/241R ;
416/204A; 416/223A; 416/244R; 420/451 |
Current CPC
Class: |
C23C 8/20 20130101; Y10T
29/49746 20150115; Y10T 29/4932 20150115; Y10T 29/49336 20150115;
Y10T 29/49337 20150115; Y10T 29/49339 20150115; Y10T 29/49229
20150115; C23C 8/80 20130101 |
Class at
Publication: |
416/241.R ;
416/204.A; 416/223.A; 416/244.R; 420/451 |
International
Class: |
F01D 5/14 20060101
F01D005/14; F01D 5/02 20060101 F01D005/02; F01D 5/28 20060101
F01D005/28; F01D 5/30 20060101 F01D005/30; C22C 19/03 20060101
C22C019/03 |
Claims
1. A gas turbine engine component comprising: a compressor disk and
an airfoil in frictional contact, where one or both of the
compressor disk and airfoil comprises a titanium-containing alloy
having a surface layer comprising one or more of carbides and
interstitial carbon, the surface layer having a pre-selected
thickness from the surface, and wherein the surface layer has a
sufficient amount of carbon and a sufficient thickness to resist
fretting between the compressor disk and airfoil.
2. The component of claim 1, wherein the compressor disk comprises
an alloy selected from the group consisting of Ti-6-4, Ti-17,
Ti-6-2-4-2, and titanium-containing nickel-based superalloys.
3. The component of claim 1, wherein the airfoil comprises an alloy
selected from the group consisting of Ti-6-4, Ti-4-4-2, Ti-6-2-4-2,
Ti-8-1-1 and titanium-containing nickel-based superalloys.
4. The component of claim 1, wherein both the compressor disk and
airfoil comprise the surface layer.
5. The alloy of claim 1, wherein the pre-selected distance is up to
about 0.01 inches.
6. The alloy of claim 5, wherein the pre-selected distance is up to
about 0.001 inches.
7. The alloy of claim 1, wherein a coefficient of friction of up to
about 0.6 is present between the compressor disk and airfoil.
8. A gas turbine engine component comprising: a titanium-containing
surface having a surface layer containing one or more of carbides
and interstitial carbon, the surface further comprising a lubricant
coating having a binder and a friction modifier; and wherein the
coefficient of friction between the surface and another
titanium-containing surface is less than about 0.6 in high altitude
atmospheres.
9. The component of claim 8, wherein the component is selected from
the group consisting of a compressor disk and an airfoil.
10. The component of claim 8, wherein the friction modifier
comprises a material selected from the group consisting of tungsten
sulfide, bismuth telluride, bismuth oxide and combinations
thereof.
11. The component of claim 10, wherein the friction modifier
comprises tungsten sulfide.
12. The component of claim 8, wherein the binder comprises a
material selected from the group consisting of titanium oxide,
aluminum phosphate and combinations thereof.
13. The component of claim 12, wherein the binder comprises
titanium oxide.
14. The component of claim 8, wherein the coefficient of friction
between the surface and another titanium-containing surface is less
than about 0.4 in high altitude atmospheres.
15. The component of claim 8, wherein the coefficient of friction
between the surface and another titanium-containing surface is less
than about 0.2 in high altitude atmospheres.
16. The component of claim 8, wherein the high altitude atmospheres
include up to about 800.degree. F.
17. The component of claim 8, wherein the high altitude atmospheres
include an atmosphere substantially devoid of water vapor.
18. The component of claim 8, wherein the titanium-containing
surface includes an 5 alloy selected from the group consisting of
Ti-6-4, Ti-17, Ti-4-4-2, Ti-6-2-4-2, Ti-8-1-1 and
titanium-containing nickel-based superalloys.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 11/247,686, filed Oct. 11, 2005, which is incorporated by
reference in its entirety and which claims the benefit of U.S.
Provisional Application No. 60/694,759, filed Jun. 28, 2005.
FIELD OF THE INVENTION
[0002] The present invention is directed to a method for surface
treating titanium and titanium alloys. In particular, the invention
is drawn to surface treating gas turbine engine components.
BACKGROUND OF THE INVENTION
[0003] A gas turbine engine generally operates by pressurizing air
in a compressor and mixing the air with fuel in a combustor. The
air/fuel mixture is ignited and hot combustion gasses result, which
flow downstream through a turbine section. The compressor typically
includes compressor disks having airfoils dovetailed into the
compressor disk. The compressor may include multiple disks, each
having a plurality of airfoils.
[0004] Each of the compressor disk and the airfoils typically
contain titanium, usually in the form of a titanium alloy. The
titanium-to-titanium surface contact is susceptible to fretting
wear and fretting fatigue. Fretting is the degradation of the
surface usually resulting from localized adhesion between the
contacting surfaces as the surfaces slide against each other. The
problem of fretting is magnified in systems having a
titanium-containing surface contacting another titanium-containing
surface. For example, in a titanium compressor disk and titanium
airfoil system, the fretting fatigue may result from movement of
the dovetail of the airfoil within the slot in the compressor disk.
As the disk rotates at a higher rotational speed, the centrifugal
force on the airfoil urges the blade to move outward and slip along
the surface of the dovetail. As the disk rotates at a lower
rotational speed, the centrifugal force on the airfoil is less and
the airfoil may slip inward toward the compressor disk. A second
source of movement resulting in fretting fatigue in the dovetail
system is the vibration from the airfoil. Aerodynamic forces may
result in oscillation of the airfoil within the dovetail slot. The
oscillation translates to high frequency vibration through the
airfoil to the dovetail portion of the airfoil. As the airfoil
vibrates, the surface of the dovetail section of the airfoil slides
against the surface of the slot of the compressor disk, resulting
in fretting fatigue.
[0005] In an attempt to solve the fretting wear and fatigue
problem, the titanium dovetail surface of the airfoil may be
shot-peened to create compressive stress in the airfoil surface.
The increased compressive stress on the surface results in
increased hardness, which reduces the adhesion between surfaces
thereby reducing the fretting fatigue and wear. However, the
shot-peening process requires expensive equipment additional
processing steps and may result in surfaces having variability in
roughness and dimensional accuracy. In addition, the shot-peened
surface provides insufficient resistance to fretting fatigue and
wear.
[0006] In another attempt to solve the fretting wear and fatigue
problem, a coating of CuNiIn, aluminum bronze or a MoS.sub.2
lubricant may be coated onto the airfoil's dovetail surface to
provide a surface that experiences less adhesion between surfaces.
The application of lubricants such as MoS.sub.2 provides some
protection from localized adhesion initially, but lubricants and
lubricant coating wear away or deteriorate under service conditions
for a gas turbine engine. The reduced adhesion acts to reduce
fretting fatigue and wear, but does not provide reduced adhesion
throughout the operational conditions of the compressor
disk/airfoil system. The conventional lubricant coatings also
eventually lead to material transfer between the surfaces. In
addition, the coated dovetail surface provides insufficient
resistance to fretting fatigue and wear.
[0007] Carburizing is a method that has been used to increase
hardness of a surface. It is a well-known method for hardening
steel surface to improve wear properties. Known carburizing methods
take place at high temperatures, including temperatures of greater
than about 1700.degree. F. (927.degree. C.). High temperature
carburization methods suffer from the drawback that the method
requires expensive, specialized equipment, capable of operating
under high temperatures. Thermal treatments of blade dovetails and
disks preclude use of conventional carburizing practices.
[0008] What is needed is an inexpensive, low-temperature titanium
treatment that reduces fretting fatigue and wear that does not
suffer from the drawbacks of the prior art.
SUMMARY OF THE INVENTION
[0009] The present invention includes a method for surface treating
a gas turbine engine component comprising a titanium or titanium
alloy. The method includes providing a gas turbine engine component
having a titanium-containing surface. The component is heated to a
temperature sufficient to diffuse carbon into the titanium and
below 1000.degree. F. The surface is contacted with a
carbon-containing gas to diffuse carbon into the surface to form
carbides. Thereafter, the carbide-containing surface is coated with
a lubricant comprising a binder and a friction modifier. The binder
preferably including titanium oxide and the friction modifier
preferably including tungsten disulfide. The coefficient of
friction between the surface and another titanium-containing
surface is less than about 0.6 in high altitude atmospheres.
[0010] In accordance with the present invention, a metallic surface
comprising titanium is carburized, under controlled conditions,
using carbon-containing gases, such as methane, propane, ethylene
or acetylene gas or combinations thereof as the carburizing agent
in order to form stable carbides at a controlled, preselected
distance below the surface and/or absorb the carbon interstitially
in the titanium matrix. The carbides formed in the surface harden
the surface, providing a reduced coefficient of friction, and
reducing fretting.
[0011] Another embodiment of the present invention includes a gas
turbine engine component having a titanium-containing compressor
disk. The compressor disk including a surface containing carbides
and a lubricant coating thereon having a binder and a friction
modifier. The binder preferably including titanium oxide and the
friction modifier preferably including tungsten disulfide.
[0012] Another embodiment of the present invention includes a gas
turbine engine component having a titanium-containing airfoil. The
airfoil including one or more surfaces that contain carbides and a
lubricant coating thereon. The lubricant coating includes a binder
and a friction modifier. The binder preferably including titanium
oxide and the friction modifier preferably including tungsten
disulfide.
[0013] While the present invention contemplate the formation of
titanium carbide, titanium alloys may include other carbide forming
elements, such as, for example, vanadium. For example, alloys
containing vanadium treated according to the present invention may
include vanadium carbides, in addition to titanium carbides.
[0014] One advantage of the present invention is that the method
according to the present invention decreases the susceptibility of
the surface to fretting.
[0015] Another advantage of the present invention is that the
method according to the present invention provides a hardened
surface having carbides and/or interstitial carbon, which resist
corrosion.
[0016] Another advantage of the present invention that the method
according to the present invention provides a hardened surface that
is resistance to erosion.
[0017] Another advantage of the present invention is that the
carburization takes place at a low temperature, below 1000.degree.
F., which reduces the cost of equipment required to produce the
carburized zone.
[0018] Another advantage of the present invention is that the
surfaces subjected to fretting wear and fatigue may be replaced
less often, decreasing servicing cost and reliability.
[0019] 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
[0020] FIG. 1 is a cutaway view of a section of a known
high-pressure compressor for a turbine engine according to the
present invention.
[0021] FIG. 2 shows a perspective view of a compressor disk
according to an embodiment of the present invention.
[0022] FIG. 3 shows a cutaway view of an airfoil dovetail
positioned in a slot of a compressor disk according to the present
invention.
[0023] FIG. 4 shows an enlarged cross-sections taken from FIG. 3
showing an embodiment of the present invention.
[0024] FIG. 5 shows an enlarged cross-sections taken from FIG. 3
showing an alternate embodiment of the present invention.
[0025] FIG. 6 shows an enlarged cross-sections taken from FIG. 3
showing an alternate embodiment of the present invention.
[0026] FIG. 7 shows an enlarged cross-sections taken from FIG. 3
showing an alternate embodiment of the present invention.
[0027] FIG. 8 shows an enlarged cross-section taken from FIG. 3
showing an alternate embodiment of the present invention.
[0028] FIG. 9 shows an enlarged cross-section taken from FIG. 3
showing an alternate embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0029] FIG. 1 is a cutaway view of a section of a high-pressure
compressor for a turbine engine according to the present invention.
The compressor includes a plurality of blades 100. The blades 100
include an airfoil 101 and a dovetail 103, which is positioned
within dovetail slots 105 in a compressor disk 107. The dovetail
103 of the blade 100 retains the blade 100 during operation of the
gas turbine engine. The blade 100 and the compressor disk 107
according to the invention include titanium and have one or more
surfaces that are in frictional contact that are carburized to
produce a surface having a carburized zone 401 (see FIGS. 4-9). In
addition, one or more of the surfaces of the dovetail 103 and
dovetails slots 105 of the compressor disk 107 are coated with a
lubricant coating 601 (see FIGS. 6-9).
[0030] FIG. 2 shows a perspective view of a compressor disk 107
according to an embodiment of the present invention, wherein FIG. 2
shows dovetail slots 105 into which the dovetail 103 section of
blades 100 are positioned. The surfaces of dovetail slots 105 are
subjected to sliding friction with dovetail 103 of blades 100 and
are susceptible to fretting. The surface of compressor disk 107
includes a carburized zone 401 and, preferably, a lubricant coating
601 (see FIGS. 4-9).
[0031] FIG. 3 shows a cutaway view of a blade 100 positioned in
dovetail slots 105 of compressor disk 107 according to an
embodiment of the present invention. At least a portion of the
surface of slot 105 is in frictional contact with at least a
portion of the surface of dovetail 103. As the gas turbine engine
operates, the centrifugal forces provided by the variation of the
rotational speed of the compressor disk 107 results in rubbing
between the surface of the dovetail 103 and the surface of the
dovetail slot 105 in the compressor disk 107. The coefficient of
friction between the surfaces of the dovetail 103 and the surface
of the slot 105 are preferably maintained below 0.6. Preferably,
the coefficient of friction is below 0.4. More preferably, the
coefficient of friction is below 0.2. The lowering of the
coefficient of friction is a result of the hardened surface
resulting from the carburization. The carburized zone 401 (see
FIGS. 4-9) has a greater hardness than an untreated
titanium-containing surface. In addition, the application of a
lubricant coating 601 (see FIGS. 6-9) further decreases the
coefficient of friction. The additional lowering of the coefficient
of friction is a result of the tribological properties of
components of the lubricant coating 601.
[0032] FIGS. 4-9 shows enlarged cross-sections taken from region
301 from FIG. 3 illustrating alternate coating arrangements
according to the present invention. The cross sections in FIGS. 4-9
each include a dovetail slot 105 of compressor disk 107 and
dovetail 103 in frictional contact. The surface of the dovetail
slot 105 of compressor disk 107 and the surface of the dovetail 103
form opposed surfaces onto which a carburized zone 401 and
lubricant coating 601 may be applied. FIGS. 4-9 illustrate
alternate locations for placement of the carburized zone 401 and
lubricant coating 601. Lubricant coating 601 may be disposed on the
dovetail 103, the dovetail slot 105 of the compressor disk 107, a
carburized dovetail 103 or a carburized dovetail slot 105 of the
compressor disk 107 or on a combination thereof. A preferred
lubricant coating 601 includes, but is not limited to, tungsten
sulfide, bismuth telluride or bismuth oxide in a binder of aluminum
phosphate or titanium oxide. Although a space has been shown
between the coatings on the compressor disk 107 and the dovetail
103 in FIGS. 4-9, the space is merely illustrative of the placement
of the coatings. The coating systems on each of the surface of the
dovetail slot 105 and the dovetail 103 are in frictional contact,
wherein the surfaces are adjacent and experience sliding or
rubbing. Also, FIGS. 4-9 are shown having thicknesses of the
carburized zone 401 and lubricant coating 601 that is merely
illustrative and does not indicate the relative thickness of the
carburization coating 401 or the lubricant coating 601.
[0033] FIG. 4 shows an enlarged cross-section taken from region 301
from FIG. 3 showing an embodiment of the present invention. FIG. 4
includes dovetail 103 interfacing with the dovetail slot 105 of
compressor disk 107. Surface 403 of the dovetail slot 105 of
compressor disk 107 and surface 409 of dovetail 103 have each been
carburized and include carburized zone 401. Surface 405 includes
the surface of the carburization coating 401 On the compressor disk
and is in frictional contact with surface 407. Surface 407 is the
surface of the carburized zone 401 on surface 409 of dovetail 103.
The embodiment shown in FIG. 4 has the benefit that carburized zone
401 is provided on both the dovetail and compressor disk 107
providing hardened sliding surfaces that slide against each other
providing desirable tribological properties. In particular, the
combination of the hard, wear resistant carburized zone 401 sliding
against each other provide a low coefficient of friction and
increased fretting resistance.
[0034] FIG. 5 shows an enlarged cross-section taken from region 301
from FIG. 3 showing an alternate embodiment of the present
invention. FIG. 5 includes dovetail 103, dovetail slot 105 of
compressor disk 107, as shown in FIG. 4. Surface 403 of the
dovetail slot 105 of compressor disk 107 has been carburized and
includes carburized zone 401. Surface 405 includes the surface of
the carburized zone 401 on the dovetail slot 105 on compressor disk
107 and is in frictional contact with surface 409 of dovetail 103.
The embodiment shown in FIG. 5 has the benefit that the carburized
zone 401 is coated only on the compressor disk 107. Therefore, the
application of carburized zone 401 requires less equipment and
labor than applying carburized zone 401 to both the compressor disk
107 and the blade 100.
[0035] FIG. 6 shows an enlarged cross-section taken from region 301
from FIG. 3 showing an alternate embodiment of the present
invention. FIG. 6 includes dovetail 103, dovetail slot 105 of
compressor disk 107, as shown in FIG. 4. Surface 403 of the
dovetail slot 105 of compressor disk 107 has been carburized and
includes carburized zone 401. Lubricant coating 601 is disposed on
surface 405 of the carburized zone 401. Surface 603 of lubricant
coating 601 is in frictional contact with surface 409 of dovetail
103. The embodiment shown in FIG. 6 has the benefit that the
carburized zone 401 and lubricant coating 601 are coated only on
the compressor disk 107. Therefore, the production of carburized
zone 401 requires less equipment and labor than producing
carburized zone 401 to both the dovetail slot of compressor disk
107 and the airfoil. In addition, the compressor disk 101 is
protected from fretting damage, whereas the cheaper airfoil 101 has
not been specially treated. The carburized zone 401 and lubricant
coating 601 provide protection of the compressor disk 107 and
airfoil 101 system, while not adding expense to the blades 100.
[0036] FIG. 7 shows an enlarged cross-section taken from region 301
from FIG. 3 showing an alternate embodiment of the present
invention. FIG. 7 includes dovetail 103, dovetail slot 105 of
compressor disk 107, as shown in FIG. 4. Surface 403 of dovetail
103 of blade 100 has been carburized and includes carburized zone
401. Lubricant coating 601 is disposed on surface 407 of the
carburized zone 401. Surface 603 of lubricant coating 601 is in
frictional contact with surface 403 of the dovetail slot 105 of
compressor disk 107. The embodiment shown in FIG. 7 has the benefit
that the carburized zone 401 and lubricant coating 601 are coated
only on dovetail 103 of blade 100. Coating only the dovetail 103
has the advantage that the blades 100 may easily be removed from
the compressor disk 107 in order to be coated according to the
present invention. The compressor disk 107 and blade 100 system of
the present invention may be retrofitted into existing gas turbine
engines by removing the blades 100 from the compressor disks 107,
wherein the removal of the compressor disk 107 from the engine is
not necessary. In this embodiment, the dovetail 103 may provide the
resistance to fretting without requiring the removal or replacement
of the compressor disks 107 from the engine.
[0037] FIG. 8 shows an enlarged cross-section taken from region 301
from FIG. 3 showing an alternate embodiment of the present
invention. FIG. 8 includes dovetail 103, dovetail slot 105 of
compressor disk 107, as shown in FIG. 4. Surface 403 of the
dovetail slot 105 of compressor disk 107 has been carburized and
includes carburized zone 401. Lubricant coating 601 is disposed on
surface 409 of the dovetail 103. Surface 603 of lubricant coating
601 is in frictional contact with surface 405 of carburized zone
401 on the dovetail slot 105 of compressor disk 107. The embodiment
shown in FIG. 8 has the benefit that the carburized zone 401 is
present on the dovetail slot 105 of compressor disk 107 protecting
the surface from fretting. In addition, the dovetail 103 of blade
100 is coated with lubricant coating 601. The lubricant coating 601
may be easily replaced by removing the blade 100 from compressor
disk 107 and coating the lubricant coating 601 onto dovetail 103 of
blade 100. The lubricant coating 601 in this embodiment permits the
easy replacement of the lubricant coating 601 in the event that the
lubricant coating 601 wears thin or wears completely off.
[0038] FIG. 9 shows an enlarged cross-section taken from region 301
from FIG. 3 showing an alternate embodiment of the present
invention. FIG. 9 includes dovetail 103, dovetail slot 105 of
compressor disk 107, as shown in FIG. 4. Surface 403 of dovetail
slot 105 of compressor disk 107 has been carburized and includes
carburized zone 401. Surface 409 of dovetail 103 of blade 100 has
also been carburized and includes carburized zone 401. Lubricant
coating 601 is disposed on surface 407 of the carburized coatings
401, both on the dovetail 103 of blade 100 and on the dovetail slot
105 of compressor disk 107. Surface 603 of lubricant coating 601 on
the carburized zone 401 on the dovetail slot 105 of compressor disk
107 is in frictional contact with surface 603 of lubricant coating
601 on the carburized zone 401 on the dovetail 103 of blade 100.
The embodiment shown in FIG. 9 has the benefit that the carburized
coating 401 and lubricant coating 601 are present on both the
dovetail 103 of blade 100 and on the dovetail slot 105 on
compressor disk 107, providing addition protection against fretting
on both surfaces. In this embodiment, the coatings have additional
protection against the lubricant coating 601 wearing off due to the
two lubricant coatings 601. In addition, this embodiment permits
the opposed hard, wear resistant carburized zone 401 surfaces to
slide against each other provide a low coefficient of friction and
increased fretting resistance with the addition fretting resistance
provided by the lubricant coatings 601 disposed thereon.
[0039] The present invention also provides methods for carburizing
a metallic surface comprising titanium. In a preferred embodiment,
titanium-containing blade 100 or compressor disk 107 for use in a
gas turbine engine is subjected to carburizing. The compressor disk
107 or airfoil according to the present invention is preferably a
titanium alloy. In one embodiment of the invention, the compressor
disk 107 or blade 100 is Ti-6-4 titanium alloy having about 6 wt %
aluminum, about 4 wt % vanadium and balance essentially titanium.
Other suitable alloys for use in the blade 100 include, but are not
limited to Ti-4-4-2 (about 4 wt % aluminum, about 4 wt %
molybdenum, and about 2 wt % tin), Ti-6-2-4-2 (about 6 wt %
aluminum, about 2 wt % molybdenum, about 4 wt % zirconium and about
2 wt % tin), Ti-8-1-1 (about 8 wt % aluminum, about 1 wt %
molybdenum, and about 1 wt % vanadium). Other suitable alloys for
use in the compressor disk 107 include, but are not limited to
Ti-17 (about 5 wt % aluminum, about 4 wt % chromium, about 4 wt %
molybdenum, about 2 wt % zirconium and about 2 wt % tin) and
Ti-6-2-4-2 (about 6 wt % aluminum, about 2 wt % molybdenum, about 4
wt % zirconium and about 2 wt % tin). Other suitable alloys for
fabrication of compressor disk 107 for use with blades 100 having a
carburized zone 401 include, but are not limited to, nickel-based
alloys, such as INCONEL.RTM. 718, R-includes carburized zone 401.
Lubricant coating 601 is disposed on surface 407 of the carburized
coatings 401, both on the dovetail 103 of blade 100 and on the
dovetail slot 105 of compressor disk 107. Surface 603 of lubricant
coating 601 on the carburized zone 401 on the dovetail slot 105 of
compressor disk 107 is in frictional contact with surface 603 of
lubricant coating 601 on the carburized zone 401 on the dovetail
103 of blade 100. The embodiment shown in FIG. 9 has the benefit
that the carburized coating 401 and lubricant coating 601 are
present on both the dovetail 103 of blade 100 and on the dovetail
slot 105 on compressor disk 107, providing addition protection
against fretting on both surfaces. In this embodiment, the coatings
have additional protection against the lubricant coating 601
wearing off due to the two lubricant coatings 601. In addition,
this embodiment permits the opposed hard, wear resistant carburized
zone 401 surfaces to slide against each other provide a low
coefficient of friction and increased fretting resistance with the
addition fretting resistance provided by the lubricant coatings 601
disposed thereon.
[0040] The present invention also provides methods for carburizing
a metallic surface comprising titanium. In a preferred embodiment,
titanium-containing blade 100 or compressor disk 107 for use in a
gas turbine engine is subjected to carburizing. The compressor disk
107 or airfoil according to the present invention is preferably a
titanium alloy. in one embodiment of the invention, the compressor
disk 107 or blade 100 is Ti-6-4 titanium alloy having about 6 wt %
aluminum, about 4 wt % vanadium and balance essentially titanium.
Other suitable alloys for use in the blade 100 include, but are not
limited to Ti-4-4-2 (about 4 wt % aluminum, about 4 wt %
molybdenum, and about 2 wt % tin), Ti-6-2-4-2 (about 6 wt %
aluminum, about 2 wt % molybdenum, about 4 wt % zirconium and about
2 wt % tin), Ti-8-1-1 (about 8 wt % aluminum, about 1 wt %
molybdenum, and about 1 wt % vanadium). Other suitable alloys for
use in the compressor disk 107 include, but are not limited to
Ti-17 (about 5 wt % aluminum, about 4 wt % chromium, about 4 wt %
molybdenum, about 2 wt % zirconium and about 2 wt % tin) and
Ti-6-2-4-2 (about 6 wt % aluminum, about 2 wt % molybdenum, about 4
wt % zirconium and about 2 wt % tin). Other suitable alloys for
fabrication of compressor disk 107 for use with blades 100 having a
carburized zone 401 include, but are not limited to, nickel-based
alloys, such as INCONEL.RTM. 718, R-95, or R-88. INCONEL.RTM. is a
federally registered trademark owned by Huntington Alloys
Corporation of Huntington, West Virginia. The composition of
INCONEL.RTM. 718 is well-known in the art and is a designation for
a nickel-based superalloy comprising about 18 weight percent
chromium, about 19 weight percent iron, about 5 weight percent
niobium+tantalum, about 3 weight percent molybdenum, about 0.9
weight percent titanium, about 0.5 weight percent aluminum, about
0.05 weight percent carbon, about 0.009 weight percent boron, a
maximum of about 1 weight percent cobalt, a maximum of about 0.35
weight percent manganese, a maximum of about 0.35 weight percent
silicon, a maximum of about 0.1 weight percent copper, and the
balance nickel. R-95 includes a composition having about 8% cobalt,
about 13% chromium, about 3.5% molybdenum, about 3.5% tungsten,
about 3.5% aluminum, about 2.5% titanium, about 3.5% niobium, about
0.03% boron, about 0.03% carbon, about 0.03% zirconium, up to about
0.01% vanadium, up to about 0.3% hafnium, up to about 0.01% yttrium
and the balance essentially nickel. R-88 includes a composition
having about 13% cobalt, about 16% chromium, about 4% molybdenum,
about 4% tungsten, about 2% aluminum, about 3.7% titanium, about
0.75% niobium, about 0.4% zirconium, about 0.06% carbon, about
0.010% boron and the balance essentially nickel.
[0041] In accordance with the present invention, a metallic surface
comprising titanium is carburized, under controlled conditions,
using carbon-containing gases, such as methane, propane, ethylene
gas, acetylene, carbon dioxide, carbon monoxide or combinations
thereof as the carburizing agent in order to form stable carbides
at a controlled, preselected distance below the surface. The
carbides may include titanium carbides, vanadium carbides and
mixtures thereof, including titanium-vanadium carbide complexes.
These gases may be mixed in combination, or non-reactive gases such
as argon, helium, or hydrogen may be added in order to control the
reactivity of the carburizing gases. The titanium carbide formed in
the surface hardens the surface, providing a reduced coefficient of
friction, and reducing fretting. The concentration and/or presence
of interstitial carbon in the titanium matrix can also be a
controlling factor in the process.
[0042] The present invention may include a step of cleaning the
article surface. Cleaning the article surface entails removing a
portion or substantially all oxides from the surface of the
substrate and preventing the reformation of oxides from the surface
that is to be carburized. The surface to be carburized is
preferably free of oxides. Removing oxides can be accomplished by
mechanical or chemical methods that do not damage or otherwise
adversely affect the substrate surface. The mechanical or chemical
oxide removal methods may be any oxide removal methods known in the
art, including but not limited to grit blasting or chemical
etching. After such cleaning, the surfaces may be cleaned with a
suitable solvent, while avoiding the formation of oxides. While
oxides are to be avoided, it may be desirable to mask portions of
the surface in order to prevent these portions from being
carburized. This may be desirable for any one of a number of
reasons, such as titanium containing surfaces that are not in
contact with other titanium containing surfaces and/or may not be
susceptible to fretting or wear. Therefore, when desirable, the
portion that does not require carburized may be masked.
[0043] Although masking may be provided to surface portions of the
compressor disk 107 and/or the blade 100, the carburizing of the
entire compressor disk 107 and/or blade 100 may provide the
compressor disk 107 and blade 100 with desirable surface
properties. For example, an airfoil 101 portion of a blade 100
having a carburized zone 401 may be resistant to corrosion due to
the presence of carbides and/or interstitial carbon at the surface.
The resistance to corrosion is desirable for airfoils 101 and
compressor disks 107 due to the fact that the airfoils 101 and
compressor disks may contact air that includes water and/or
corrosion accelerators, such as salt. In addition, the carburizing
of the entire compressor disk 107 and/or blade 100 may provide the
compressor disk 107 and blade 100 with protection against erosion
due to the hardened, wear-resistant carburized zone 401. The
resistance to erosion is desirable, for example, for airfoils 101
and compressor disks 107 due to contact with air that includes
abrasive material, such as sand or dirt. Therefore, the method of
the present invention may advantageously be utilized to coat the
entire compressor disk 107 and/or blade 100.
[0044] The cleaned article is then loaded into a furnace suitable
for performing the carburization process. Suitable furnaces include
vacuum furnaces or furnaces that can maintain a controlled
atmosphere. The furnace is heated to a temperature sufficient to
permit the diffusion of carbon into titanium, and less than about
1000.degree. F. (538.degree. C.). preferably, the furnace is heated
to about 750.degree. F. (400.degree. C.). After the
titanium-containing article has reached the carburization
temperature, the carburizing gases may be introduced into the
furnace by any method that prevents the introduction of oxygen. In
addition, introduction of the carburizing gases should be such that
the concentration of the carbon-containing gas may be varied. When
maintaining a controlled atmosphere, the atmosphere must be
non-oxidizing, as oxidation of the article surface and reaction of
the carburizing gas with oxygen must be prevented during heat-up to
the carburizing temperature and during carburizing. Once the
carburizing temperature is approached, the carburizing gas,
methane, propane, ethylene or acetylene, is introduced into the
furnace. These carburizing gases may be introduced below the
carburizing temperature with hydrogen or to gradually replace
hydrogen, but should not be added at temperature or in a volume
that will result in excessive soot formation. The carburizing gas
is provided to ensure sufficient carbon is present at the article
surface for desired carburization so that carbides are formed in a
layer of sufficient thickness to form titanium carbide and/or to
allow for carbon to be absorbed interstitially, to increase the
hardness of the surface and to reduce fretting. The formation of
the carbides during the carburization results in a hardening of the
surface. As the hardness of the surface increases, the incident of
localized adhesion between titanium-containing surfaces is reduced.
The reduction is localized adhesion results in a greater resistance
to fretting fatigue and wear. The duration, temperature and
concentration of carbon in the carbon-containing gas of the
carburization process may be controlled to limit the depth of
carbide layer formation.
[0045] Carburization is continued until the desired carburization
depth is reached at which time the operation is stopped by
introducing an inert gas to the furnace. Carburization ceases when
the surface temperature of the article is less than the temperature
at which carbon diffuses. The depth of the carburization varies
based upon a variety of factors including the time the article is
exposed to the carbon-containing gas, the concentration of the
carbon in the carbon-containing gas and the temperature of the
article. A preferable depth for the carburization coating 401 is up
to about 0.01 inches. More preferably up to about 0.001 inches. The
carburization process according to the invention takes place for a
time up to about 1500 hours for the desired carburization coating
401 depth to be achieved. Preferably, the carburization takes place
for a time up to about 1000 hours.
[0046] The carburization process is completed by purging the
chamber of the carburizing gas. This can be accomplished by
stopping the flow of the carburizing gas and introducing an inert
gas, nitrogen or hydrogen into the chamber. This also serves to
cool the article. Any masking present on the surface may be
removed.
[0047] As will be recognized by those skilled in the art, several
operating parameters can be varied, therefore these parameters must
be controlled to control the desired carbide layer thickness. These
parameters include, but are not limited to gas flow rate, which
determines partial gas pressure, temperature, type of furnace,
working zone size, work load and time.
[0048] After processing and cooling, the work load, may comprise a
plurality of articles, can be removed from the work zone. Any
optional masking may be removed before or after the application of
the lubricant coating 601. Masking may be removed by any suitable
means that does not adversely affect the substrate surface, such as
chemical stripping, mechanical means such as blasting, or other
known methods consistent with the masking material.
[0049] Compressor disks 107 and airfoils 101 that comprise titanium
are particularly suitable for use with the method of the present
invention. Carburized compressor disks 107 and/or dovetails 103
coated with a lubricant coating 601 provide desirable tribological
properties. The present invention utilizes the combination of the
relatively hard carburized zone 401 in combination with a
relatively soft, lubricious lubricant coating 601, which may be
placed on surfaces susceptible to wear. Suitable surfaces include
component surfaces within a compressor of a gas turbine engine. The
carburized zone 401 reduces the coefficient of friction between the
compressor disk 107 and blade 100. The lubricant coating 601
further reduces the coefficient of friction between the compressor
disk 107 and the blade 100, reducing localized adhesion between the
surfaces, thereby reducing fretting.
[0050] The coefficient of friction is preferably maintained in the
wear system of the dovetail slot 105 and dovetail 103 equal to or
less than 0.6 and preferably equal or less than 0.4. More
preferably, the coefficient of friction is maintained in the wear
system of the dovetail slot 105 and dovetail 103 equal to or less
than 0.2. The coefficient of friction is measured between the two
surfaces rubbing against each other. In the embodiments of the
present invention shown in FIGS. 4-9, the coefficient of friction
between the dovetail 103 of blade 100 and dovetail slot 105 of
compressor disk 107, is less than or equal to about 0.6. The
compressor disk 107 and blade 100 may be fabricated from any
suitable material, including but not limited to metals and metal
alloys. Preferred materials include titanium and its alloys. Other
suitable alloys include, but are not limited to, nickel-based
alloys, such as INCONEL.RTM. 718. In addition, compressor disks 107
may be fabricated from nickel-based alloys, such as R-95 and
R-88.
[0051] The lubricant coating 601 comprises a binder, a friction
modifying agent, and, optionally, an additive. The binder of the
lubricant coating 601 comprises a material selected from the group
consisting of sodium silicate, aluminum phosphate, titanium oxide
and combinations thereof. The friction-modifying agent is
preferably dispersed substantially uniformly through the binder.
The lubricant coating 601 reduces the coefficient of friction
between the dovetail slot 105 of compressor disk 107 and the
dovetail 103 of blade 100. Of the antifriction coating binders,
aluminum phosphate and titanium oxide are preferred. As the gas
turbine engine and the compressor operate, lubricant coating 601
may eventually be consumed due to the sliding of the surfaces. The
lubricant coating 601 is resilient and regenerates in areas where
the coating is rubbed thin or cleaned off the wear surface. The
lubricant coating 601 is thin when the thickness on a portion of
the surface is insufficient to provide sufficient lubricity to the
sliding surfaces to maintain the coefficient of friction at the
desired level. In addition, during operation, the lubricant coating
601 may migrate from location to location along the sliding
surfaces. The migration of the lubricant coating 601 allows areas
that have less material or are rubbed completely off to receive
lubricant coating material from other locations along the wear
surface to regenerate the coating missing from the area rubbed thin
or completely off.
[0052] The binder material for use in the lubricant coating 601 is
any binder material that is tribologically compatible with all of
the following materials: 1) water, 2) detergents used in the
cleaning of gas turbine engine parts, 3) deicers known in the art
used to device aircraft in winter, 4) aircraft fuel, 5) oil and 6)
hydraulic fluid. The materials are tribologically compatible if the
binder in the lubricant coating 601 maintains tribological
properties (e.g., lubricity and wear resistance) of the lubricant
coating 601 when in contact with the surfaces subjected to sliding
friction and in contact with the materials listed above. In order
to maintain tribological properties, the binder exhibits the
ability to remain coated on the substrate, does not result in
separation of the friction modifier and the binder, and does not
result in substantial softening of the antifriction coating.
Suitable binder materials include, but are not limited to, sodium
silicate, aluminum phosphate, titanium oxide and combinations
thereof. Binders that provide the highest tribological
compatibility include titanium oxide and aluminum phosphate.
[0053] The friction modifier is any material that, when added to
the binder, produces a friction coefficient suitable for
maintaining desirable tribological properties within the compressor
of a gas turbine engine. In addition to reducing the amount of
fretting that takes place between the dovetail 103 of the airfoil
101 and the compressor disk 107, the lubricant coating 601 ideally
should withstand the operating conditions of the compressor,
including high altitude atmosphere, including atmospheres devoid of
water vapor, and high temperatures. The high altitude atmospheres
include atmospheres to which aircraft are exposed during flight.
The high altitude atmosphere includes atmospheres having reduced or
no water vapor, which causes lubricants containing graphite to lose
their effectiveness as a lubricant. High temperature exposure is a
result of the operation of the gas turbine engine. The compression
of the gas and the combustion of the fuel result in high
temperatures in gas turbine engines. Parts within the gas turbine
engine, including the components of the compressor, may be subject
to high temperatures. The coating system, including the carburized
zone 401 and lubricant coating 601 of the present invention may
find uses in parts within the gas turbine engine that are exposed
to temperatures up to and in excess of about 800.degree. F.
Desirable tribological properties include, but are not limited to
low coefficient of friction between sliding surfaces (i.e., high
lubricity) and low wear between sliding surfaces. Preferred
friction modifier materials include, but are not limited to,
tungsten sulfide (e.g., WS.sub.2), bismuth telluride (e.g.,
Bi2Te3), copper sulfide (e.g., Cu.sub.2S), bismuth oxide (e.g.,
Bi.sub.2O.sub.3) and combinations thereof. Of the friction
modifiers, tungsten sulfide (e.g., WS.sub.2), bismuth telluride
(e.g., Bi.sub.2Te.sub.3) and bismuth oxide (e.g., Bi.sub.2O.sub.3)
are preferred.
[0054] The presence of the combination of the lubricant coating 601
and the carburized zone 401 permits the operation of the compressor
having reduced fretting even is systems that do not have the most
preferred friction modifier. For example, in less preferred
lubricant coating systems, such as a system containing graphite on
top of the carburized zone 401, the carburized zone 401 maintains a
lower coefficient of friction even in the absence of water vapor,
due to the hardened surface. Therefore, the lubricant coating 601
and carburized zone 401 combination may provide reduced fretting
even in systems having lubricant coating 601 that do not perform
well in atmospheres devoid of water vapor.
[0055] Table 1 shows examples of lubricant coating materials
according to the present invention. The examples shown are merely
examples and do not limit the invention to the combinations of
binders and friction modifiers shown therein. Examples 1-5, shown
in Table 1, include coefficient of friction (COF) results for
particular friction modifier and binder combinations. In order to
determine the coefficient of friction, the lubricant coating
materials are subject to a sliding wear test as known in the art.
The tests were conducted with a reciprocating stroke length of
0.060 inches. Lubricant coating material (i.e., inert material,
binder and friction modifier) were loaded onto the wear surfaces
and dried to form an antifriction coating 601. The coated wear
surfaces were then subject to a load of 50 lbs. and reciprocation
motion. The coefficients of friction were measured at various
temperatures during the test and an average coefficient (i.e., Avg
COF) of friction was calculated as the coefficient of friction for
the wear system. Table 1 shows the an average coefficient of
friction for each example having the average coefficient of
friction resulting from tests run at various friction modifier to
binder loadings. The lubricant coating 601 was formed from drying a
composition on the test surface having a binder loading of 10% by
weight and friction modifier loadings of from 15% by weight to 25%,
corresponding to friction modifier to binder weight ratios of from
1.5:1 to about 2.5:1. The balance of the composition is of
essentially inert material that is removed during drying.
TABLE-US-00001 TABLE 1 Friction COF Binder Modifier COF room COF at
COF at Avg Ex. 10% 15/20/25% initial temp. 400.degree. F.
750.degree. F. COF 1 titanium tungsten 0.2 0.5 0.4 0.6 0.43 oxide
sulfide 2 titanium bismuth 0.3 0.7 0.7 0.6 0.58 oxide telluride 3
titanium bismuth 0.2 0.7 0.7 0.6 0.55 oxide oxide 4 titanium copper
0.3 0.6 0.7 0.6 0.55 oxide sulfide 5 aluminum tungsten 0.3 0.4 0.5
0.5 0.43 phosphate sulfide
[0056] The friction modifier is preferably incorporated into
lubricant coating 601 in a quantity of about 10% to about 500% by
weight of binder. More preferably, the friction modifier is
incorporated into the lubricant coating 601 from 100% to about 350%
by weight of binder. The friction modifier is incorporated into the
binder material and is preferably encapsulated in the binder
material. Encapsulation may take place using any suitable
encapsulation method, including but not limited to powder
metallurgical encapsulation methods. The lubricant coating 601
including the binder and friction modifier is coated onto the
surfaces subject to wear (i.e., wear surface). Suitable methods for
coating include, but are not limited to, spraying or dipping the
surface to be coated with a lubricant coating 601 and subsequently
drying the lubricant coating 601, removing at least some of the
inert material present. The dried surface forms a lubricant coating
601 that is tenacious and substantially uniform across the wear
surface. Optionally, the lubricant coating 601 may be heated during
the drying step. Table 2 shows the average coefficient of friction
and wear in inches for various friction modifier loadings in the
lubricant coating composition. In addition, Table 2 shows the
average number of sliding cycles (i.e. reciprocations) used in
Examples 6-11 at room temperature, 400.degree. F. (204.degree. C.),
and 750.degree. F. (399.degree. C.), which resulted in the average
wear shown.
TABLE-US-00002 TABLE 2 Friction Binder Modifier Modifier to Average
Average - (10% Friction Loading Binder Weight Avg Wear Sliding Ex.
Loading) Modifier (%) Ratio COF (inches) Cycles 6 titanium tungsten
25 2.5:1 0.47 0.001- 575,000 oxide sulfide 0.005 7 titanium
tungsten 30 3.0:1 0.59 0.001- 600,000 oxide sulfide 0.005 8
titanium tungsten 35 3.5:1 0.40 0.001- 625,000 oxide sulfide 0.005
9 titanium bismuth 25 2.5:1 0.59 0.001- 350,000 ox telluride 0.004
oxide 10 titanium bismuth 30 3.0:1 0.54 0.001- 362,500 oxide
telluride 0.004 11 titanium bismuth 35 3.5:1 0.55 0.001- 312,500
oxide telluride 0.004
[0057] Although the average shown in Table 2 range from 350,000 to
635,000 cycles, in each of Examples 6-11, 1,000,000 sliding cycles
were made at 750.degree. F. (399.degree. C.).
[0058] The dovetail slot 105 and dovetail 103 system of the present
invention with the carburized zone 401 and lubricant coating 601
combination on one or both of the opposed surfaces, is preferably
resistant to wear over the entire operating temperature range of
the gas turbine engine compressor. In one embodiment of the present
invention, the opposed surfaces wear less than about 0.005 inches
after at least 500,000 reciprocations (i.e., cycles). In another
embodiment, the carburized zone 401 and lubricant coating 601
combination according to the present invention results in wear to
the vane assembly of less than about 0.005 inches over 2 million
reciprocations (i.e., cycles) at temperatures up to about
800.degree. F., where each cycle or reciprocation comprises one
movement in the reciprocating back and forth motion.
[0059] The dovetail slot 105 and dovetail 103 combination
preferably maintains a friction coefficient between the sliding
surfaces at or below about 0.6 over the entire operating range of
the compressor. More preferably, the dovetail slot 105 and dovetail
103 combination of the present invention maintains a friction
coefficient between the sliding surfaces of below about 0.5. In
particular, the surface of compressor disk 107 in contact with
blade 100 of the present invention preferably maintains a
coefficient of friction of less than about 0.5 when in contact with
the blade 100 in a reciprocating motion under a load at
temperatures up to 800.degree. F. (427.degree. C.).
[0060] In another embodiment of the present invention, additives
may be included in the lubricant coating 601 to provide additional
desirable properties for the coating system. The additional
additive is an additive that provides desirable properties, such as
increased lubricity, increased adhesion of the lubricant coating
601 to the surface, or increased coating uniformity, to the
composition. Suitable additional additives include, but are not
limited to, polytetrafluoroethylene, adhesion promoters, dispersing
agents and combinations thereof. Examples of additional additives
include graphite, molybdenum sulfide, molybdenum diselenide and
copper.
[0061] Alternate systems that find use with the present invention
include titanium-containing components of the gas turbine engine,
including actuator mechanisms, dovetail surfaces elsewhere in the
engine and other surfaces where a low coefficient of friction is
required or desirable. In particular, the present invention finds
use in applications susceptible to fretting, including applications
where one titanium-containing surface slides against a second
titanium-containing surface. Treatment of one or both of the
surfaces in frictional contact reduces the coefficient of friction,
while also reducing fretting fatigue and wear.
[0062] 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.
* * * * *