U.S. patent application number 11/272167 was filed with the patent office on 2007-05-10 for electrostatic spray for coating aircraft engine components.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. Invention is credited to Matthew Bernard Buczek, Jane Ann Murphy, Mark Rechtsteiner, Andrew Jay Skoog.
Application Number | 20070104886 11/272167 |
Document ID | / |
Family ID | 37685730 |
Filed Date | 2007-05-10 |
United States Patent
Application |
20070104886 |
Kind Code |
A1 |
Buczek; Matthew Bernard ; et
al. |
May 10, 2007 |
Electrostatic spray for coating aircraft engine components
Abstract
Electrostatic deposition of high performance powdered materials
onto gas turbine surfaces. The process also includes
post-deposition thermal staging of the deposited powder to provide
a durable coating that will satisfy the demands of turbine engine
operation. The process envisions application of organic-based
powdered materials, glass/ceramic powdered materials and
metal-based powdered materials and combinations thereof using
electrostatic techniques to components exposed to low temperature
operations, such as may be found in the front section of a gas
turbine engine or to the exterior portions of an aircraft engine,
and metal-containing glass ceramics, glass-ceramic materials, or
materials that can be transformed into glass ceramic materials,
when applied to components exposed to high temperature operations,
such as may be found in the turbine and exhaust sections of a gas
turbine engine or the flaps of an aircraft.
Inventors: |
Buczek; Matthew Bernard;
(Hamilton, OH) ; Skoog; Andrew Jay; (West Chester,
OH) ; Rechtsteiner; Mark; (Cincinnati, OH) ;
Murphy; Jane Ann; (Franklin, 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: |
37685730 |
Appl. No.: |
11/272167 |
Filed: |
November 10, 2005 |
Current U.S.
Class: |
427/458 |
Current CPC
Class: |
B05B 5/1683 20130101;
C23C 4/18 20130101; C23C 4/12 20130101; B05B 5/032 20130101; C23C
24/00 20130101; B05B 14/48 20180201; Y02T 50/60 20130101 |
Class at
Publication: |
427/458 |
International
Class: |
H05C 1/00 20060101
H05C001/00; B05D 1/04 20060101 B05D001/04 |
Claims
1. A method for coating an aircraft engine component, comprising
the steps of: providing a gas turbine engine component; providing a
high performance powder for coating the gas turbine engine
component, the powder capable of being electrostatically charged;
providing a high voltage powder spray gun; establishing a
predetermined electrical potential between the powder spray gun and
the gas turbine engine component; charging the high performance
powder while simultaneously spraying the powder at a predetermined
flow rate onto at least a portion of surface of the gas turbine
engine component to achieve a coating of predetermined thickness;
and heat treating the coated component to a temperature sufficient
to establish a strong bond between the component surface and the
coating.
2. The method of claim 2 wherein the step of heat treating the
coated component includes heat treating the coated component to a
temperature sufficient to establish a strong metallurgical bond
between the component surface and the coating.
3. The method of claim 1 wherein the step of heat treating includes
heat treating the coated component at a temperature of at least
about 1500.degree. F.
4. The method of claim 1 wherein the step of heat treating includes
firing the component to a temperature of 1500.degree. F. in a time
of about 6 minutes.
5. The method of claim 1 wherein the step of providing a high
performance powder includes providing a powder selected from the
group consisting of metal powders, organic-based powders,
ceramic-based powders and combinations thereof.
6. The method of claim 1 wherein the step of providing a high
performance powder includes providing a coated metal powder.
7. The method of claim 6 wherein the step of providing a high
performance powder includes providing MCrAlX powders, the powders
coated with a coating, where X is an element selected from the
group consisting of gamma prime formers, solid solution
strengtheners, grain boundary strengtheners, reactive elements and
combinations thereof and M is an element selected from the group
consisting of Fe, Co, Ni and combinations thereof.
8. The method of claim 7 wherein the MCrAlX powders include powders
wherein X includes at least one element selected from the group
consisting of Ta, Re Y, Zr, Hf, Si, B, C and combinations
thereof.
9. The method of claim 7 wherein the high performance powder is
NiCrAlY having an oxide coating formed over an outer surface of the
powder.
10. The method of claim 6 wherein the powders have an average size
in the range of about 5-30 microns.
11. The method of claim 1 wherein the step of providing a high
performance coating in the form of a powder further includes
providing a metal powder coated with a coating selected from the
group consisting of an inorganic binder and an oxide coating.
12. The method of claim 1 further including the step of
consolidating the coating prior to the step of heat treating the
coating when the coating of predetermined thickness is a dense
coating.
13. The method of claim 5 wherein the step of providing a high
performance powder selected from the group consisting of metal
powders, organic-based powders, ceramic-based powders and
combinations thereof further includes providing a plurality of
powders wherein at least one of the powders selected is a
binder.
14. The method of claim 13 wherein the binder is a glass frit.
15. The method of claim 13 wherein the binder powder is a
silicate-based material.
16. The binder of claim 13 wherein the binder includes aluminum
oxide particles of submicron size and smaller.
17. The method of claim 1 wherein the step of providing an aircraft
engine component includes providing at least one aircraft engine
component selected from the group consisting of a compressor
component selected from the group consisting of compressor section
components, turbine section components, combustor components and
exhaust components.
18. The method of claim 1 wherein the aircraft engine components
include turbine airfoils, shrouds, flaps, seals, liners, cowls,
center bodies and combustors.
19. The method of claim 1 wherein the step of providing a high
performance powder includes providing iron-based alloy powders.
20. The method of claim 19 wherein the iron-based alloy powders
additionally include a binder powder.
21. The method of claim 1 wherein the method of providing a gas
turbine engine component further includes providing a gas turbine
engine component wherein a portion of the gas turbine engine
component that is to be coated with a high performance coating is
coated with a bond coat.
22. The method of claim 1 wherein the step of providing a high
performance powder includes providing a plurality of layers of
powder, each layer having powders of different sizes wherein layers
having fine powders provide a higher density than layer having
coarse powders.
23. The method of claim 1 wherein the step of providing a high
performance powder further includes providing a plurality of layers
of powder, each layer having a different composition, and each
layer having a different composition having different
properties.
24. The method of claim 23 wherein the different properties include
different mechanical properties, different chemical properties,
different environmental properties and different physical
properties.
25. The method of claim 1 wherein the step of providing a high
performance powder includes providing a plurality of powders of
different composition, and the step of charging while spraying
includes charging and spraying the plurality of powders of
different compositions at the same time in the same layer.
26. The method of claim 25 wherein the step of charging and
spraying the plurality of powders of different compositions at the
same time in the same layer provides a layer having a novel
composition.
27. The method of claim 25 wherein the step of charging and
spraying the plurality of powders of different compositions at the
same time in the same layer provides a layer having a plurality of
phases.
Description
FIELD OF THE INVENTION
[0001] The present invention is directed to a method of applying a
coating to aircraft engine components, and specifically, to
applying electrostatic coatings to aircraft engine components in an
environmentally friendly fashion.
BACKGROUND OF THE INVENTION
[0002] Gas turbine engine components employ coatings over base
material in various applications to provide protection to the
underlying structural base material. The purposes for applying the
coatings are varied, and may include one or more purposes depending
upon the application. For example, turbine airfoils used in the hot
section or turbine section of a gas turbine engine include coatings
to provide heat resistance and improved thermal capabilities. These
airfoils also may be used in harsh environments, thereby
additionally requiring coatings having resistance to corrosion or
oxidation. Such coatings are referred to as environmental
coatings.
[0003] Other applications may require still other coatings. For
example, the shrouds surrounding the rotating airfoils, also
referred to as blades, form a tunnel through which the hot gases
pass. In addition to being able to withstand the hot, corrosive
gases of combustion, these shrouds must also be abradable, as the
rotating airfoils (blades) expand in a radial direction and contact
the shrouds. It is desirable that, as contact is made between the
rotating blades and the stationary shrouds that material be abraded
from the shroud without affecting the structural integrity of the
shrouds.
[0004] Of course, other sections of a gas turbine engine may
require still other coatings. For example, in an aircraft engine,
some components exposed to sand and rain may require erosion
resistance. The specialized coatings in turbine engines are myriad.
The coatings also may be applied to very large surface areas, such
as shrouds, or to very small surface area, such as the tip regions
of first stage turbine blades. The coatings also may be applied to
a variety of substrate materials, such as for example superalloy
materials, including nickel-based superalloys, cobalt-based
superalloys, iron-based superalloys and combinations thereof,
titanium and its alloys, and composites such as CMC's.
[0005] Although the structures to which the coatings are applied
may vary, a few time-tested techniques have been utilized for their
application. The techniques include a variety of modifications that
solve particular problems. However the techniques generally include
physical vapor deposition techniques (PVD), chemical vapor
deposition techniques, thermal spray techniques, pack cementation
techniques laser deposition techniques and plating techniques. A
large number of patents have issued dealing with variations of the
above-mentioned techniques, and many volumes could be filled
discussing the differences distinguishing these variations. These
techniques, including the multiple variations, typically produce
high quality coatings, as required for demanding applications such
as aircraft gas turbine techniques. However, the various techniques
used for these applications have differing drawbacks. Some of the
above-mentioned techniques, such as PVD, deposit the coating
material by a slow, expensive process. Other techniques utilize
solvents or release organic effluents, many of which are
undesirable. Others, such as laser processing, require very high
energy sources and expensive equipment. Still other processes leave
undesirable by-products, such as heavy metals, for example
chromium, which must be disposed of as hazardous waste.
[0006] What is needed is a process that can deposit a variety of
coatings on aircraft engine parts in an economical, fast, energy
efficient process that has minimal environmental impact. One method
that has heretofore not been used in gas turbine components is
powder coating based on electrostatic deposition of powdered
materials. While this method has been used for a variety of
commercial products such as home appliances, basketball poles, lawn
furniture, gas grills and certain automotive applications, the
methods have not heretofore been extended for demanding
applications such as gas turbine components, including aircraft
engine applications. It is likely that such methods have not found
their way into this art because they lack a reputation for
durability in such demanding applications.
[0007] What is needed is a durable coating for gas turbine engines
that is quick, cost effective and environmentally friendly, and
which can be readily adapted for application to both large and
small surface areas.
SUMMARY OF THE INVENTION
[0008] The present invention is directed to electrostatic
deposition of powdered materials onto gas turbine surfaces. The
process also includes post-deposition thermal staging of the
deposited powder to provide a durable coating that will satisfy the
demands of turbine engine operation.
[0009] While the present invention is directed to applying powdered
materials by electrostatic deposition, the present invention
envisions application of organic-based powdered materials,
glass/ceramic powdered materials and metal-based powdered materials
and combinations thereof using electrostatic techniques to
components exposed to low temperature operations, such as may be
found in the front section of a gas turbine engine or to the
exterior portions of an aircraft engine, and metal-containing glass
ceramics, glass-ceramic materials, or materials that can be
transformed into glass ceramic materials, to components exposed to
high temperature operations, such as may be found in the turbine
and exhaust sections of a gas turbine engine or the flaps of an
aircraft. However the present invention may also find application
in the combustor section of the engine, as well as in cooler engine
sections such as the compressor section. Aircraft engine components
that may be coated by the present process include, but are not
limited to, shrouds, flaps, seals, liners, cowls, center bodies and
combustors
[0010] The coating of the present invention is applied by
determining the proper coating material to provide the required
properties for the intended application. Then, the material is
provided as a powder in a preselected size range. The size range is
selected based on required coating thickness for the intended
application. If the size range has a high fraction of large
particles, the coating may not have the proper density. If the size
range has excessive fines, flowability may be a problem. Substrate
size and configuration may also be a consideration in determining
the size range of the particles. The powder particles are fed to a
high voltage powder spray gun. The article to be coated is grounded
and the surface is positioned facing the powder spray gun. An
electrical potential is established between the article and the
powder spray gun. As the powder is sprayed from the gun, an
electrical charge is imparted to the powder particles, which are
then drawn toward the oppositely charged surface of the article.
The polarity will depend on the types of particles that are
sprayed. Metal particles can be sprayed if the particles are
coated, either with an oxide coating or an inorganic coating,
provided that the metal powder is isolated within the coating. For
the purposes of this application, such coated metal particles will
be referred to as metal-based powders.
[0011] After the powder is applied to the article to a preselected
thickness, the article is then heat treated at an elevated
temperature sufficient to form a strong bond between the substrate
and the applied coating. When the applied coating applied using a
metal-based powder, the heat treatment temperature should be
sufficiently high so as to form a metallurgical bond between the
substrate and the applied coating. Depending upon the application
and powder size selected, it may be necessary to consolidate the
coating prior to the final heat treatment if a high density coating
is required.
[0012] An advantage of the present invention is that it can be
readily tailored to gas turbine applications, which may include a
variety of materials and surfaces of different sizes. The equipment
used in the process is readily adaptable to the different
components used in gas turbine applications. Changes in flow rates
and voltages are readily made.
[0013] Another advantage of the present invention is that a wide
variety of particle sizes can be mixed together and sprayed onto
the surface of the particle. In addition, particles of different
compositions can be mixed together and sprayed onto the article
surface. This aspect of the invention can be utilized to apply
well-known compositions or to achieve new compositions.
[0014] An important advantage of the present invention is that it
is environmentally friendly, providing very high yields while using
no solvents and less energy. Firing can be accomplished in very
short time frames. For example, firing can be accomplished to
temperatures of 1500.degree. F. in times as short as six (6)
minutes. Such rapid firing can be accomplished since no binder is
utilized; thus, no slow binder burnout is required. In addition,
the equipment, its maintenance and operation to apply the powdered
coating is inexpensive compared to other coating processes used for
gas turbine and aircraft engine applications.
[0015] The coating of the present invention can be tailored to
yield high density or low density coatings as desired. Another
advantage is that the thickness of the applied coating can also be
controlled to meet existing tolerance requirements.
[0016] Yet another advantage of the present invention is that the
powders utilized in the spray process, but which are not
incorporated onto the substrate surface, can be recovered and
reused. Thus, in terms of powder usage, the yield is well above
90%, and can approach 100%, since there is very little powder loss,
particularly in large volume applications. This is important as the
particles themselves, when they include heavy metals such as
chromium or nickel, can constitute a hazardous waste. The
reusability of the powders thus eliminates a source of hazardous
waste.
[0017] 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
[0018] FIG. 1 depicts a powder spray gun nozzle, in cross-section,
propelling a high performance powder coating at a gas turbine
engine substrate.
[0019] FIG. 2 depicts the powder spray gun nozzle of FIG. 1, in
cross-section in greater detail.
[0020] FIG. 3 schematically depicts a spray room operation using
the powder spray nozzle of FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
[0021] The method of the present invention is implemented, in its
simplest form, as depicted in FIG. 1. A powder spray gun 2, whose
partially depicted nozzle 4 includes an electrode 6. Powder
particles 8 is propelled through nozzle 4 at a surface 10 of a gas
turbine engine substrate 12. The nozzle is grounded at 14 as shown
in FIG. 1. A voltage is set up between the electrode and the
surface. As shown in FIG. 1, the electrode is negatively charged
and the substrate is positively charged. As the particles 8 are
propelled past the electrode, a charge is imparted to the particle
powders, which are additionally attracted electrostatically to
surface 10. A layer 16 of powder particles 8 forms on surface 10 of
the substrate 12. It will be understood that the polarity of the
electrode 6 and substrate 12 can be reversed as required. Such a
reversal of polarity may be desirable based on the chemistry of the
powder particles so as to improve yield. It will also be understood
that the nozzle itself may be designed as an electrode, or that the
electrode may be built into the nozzle, rather than being
positioned in the center of the nozzle orifice as depicted in FIG.
1.
[0022] The nozzle 4 of FIG. 1 is shown in greater detail in FIG. 2.
Electrode 6 is positioned at the mouth 18 of orifice 20 of nozzle
4. The mouth 18 of nozzle 4 is flared so that the volume of the
nozzle at the mouth increases. As shown, the nozzle is chamfered or
beveled. However, the flaring can be achieved by any other
geometric configuration, such as a mouth having a concave or
parabolic opening. A deflector 22 is positioned in mouth 18,
surrounding electrode 6. Powder particles traveling through orifice
20 of nozzle 4 are deflected outwardly by deflector 22 as they
reach the nozzle, a shown in FIG. 2, and also are charged by
electrode 6 as they pass through mouth 18. Electrode 6, as shown in
FIG. 2, is connected to a power source via resistive wire 24
positioned in wall 26. As previously noted, this is but one
configuration for the nozzle of a powder spray gun. Any other
configuration that imparts a charge to powder particles exiting the
nozzle may also be used.
[0023] FIG. 3 schematically depicts an exemplary embodiment of the
equipment used for the process of the invention in greater detail
in a spray room operation. A gas turbine engine substrate is
depicted mounted in a chamber 30 and connected to ground at 14.
Nozzle 4 of power spray gun 2 extends through an opening 32 in a
wall 34 of chamber 30. A high voltage power pack 38 is connected to
the powder gun 2. Powder to be sprayed is loaded from a powder
source, drum unloader 40 and provided to collector 42. Here the
powder can be sieved in sieve 44, and when appropriate, run through
a magnetic separator 46 to separate magnetic material from
non-magnetic material. Oversized material can be removed from sieve
through channel 45 and sent to a collection station (not shown.)
The powder then is moved into distribution hopper 48 and then into
feed hopper 50. From here, the powder is fed into the nozzle 4 of
gun 2. The charged powder particles are then directed toward
substrate 12. Any unused powder particles can be recovered by
passing them through to recycle bin 52, where they can be
redirected into collector 42.
[0024] To change powders, it is necessary to remove the drum from
drum unloader 40 and purge the collector 42, sieve 44, magnetic
separator 46 (if used) distribution hopper 48 and feed hopper 50,
as well as recycle bin 52 of powder. Sieve 44 can be removed and
replaced with a different size as required and a new drum a
different powder can be provided in drum unloader 40.
[0025] In accordance with the present invention, coupons
representative of aircraft engine substrates were prepared. Samples
were prepared both on bare substrates comprising superalloy
material and on substrate to which a bond coat was applied. The
bond coat was a well known NiCrAlY. Test coupons were 1''.times.4''
and 3''.times.3''. The powders sprayed were processed NiCrAl balls
sized through -400 mesh. The balls were in the size range of 5-30
microns and includes an oxide scale naturally formed by exposure to
the atmosphere.
[0026] The powder particles were fluidized at a pressure of 5-8 psi
and atomized at a pressure of 50 psi to provide a flow pressure
from the nozzle of 50 psi. A voltage of 90 kv was applied between
the nozzle and the substrate. The NiCrAlY powders were atomized
along with a binder comprising Ferro PG-94C, commonly referred to
at GROUNDCOAT.TM., a fused silicate glass frit available from Ferro
Corporation, Frit Division, 4150 East 56.sup.th Street, Cleveland,
Ohio 44101. After application, the coupons were fired at a
temperature of 1400-1650.degree. F. for a time of 4-6 minutes.
EXAMPLE 1
[0027] A 3''.times.3'' test coupon of 0.060' thick IN 625 was
prepared. The coupon was coated with a standard NiCrAlY bond coat
to a thickness of 3-12 mils. Uncoated iron-based powders and PG-94C
binder was then applied to the coupon at a thickness of about
0.013'' using the procedure set forth above, including the heat
treatment. After heat treatment, the outer strain of the coating
was measured and found to be about 0.86%. The PG-94C, discussed
above, is included in the final coating to hold other ceramic and
metal particles in place.
EXAMPLE 2
[0028] A 3''.times.3'' test coupon of 0.060' thick IN 625 was
prepared. Uncoated iron-based powder and PG-94C binder was then
applied directly to the surface of the coupon (i.e. no bond coat)
to a thickness of about 0.013'' using the procedure set forth
above, including the heat treatment. After heat treatment, the
outer strain of the coating was measured and found to be about
1.19%.
EXAMPLE 3
[0029] A 3''.times.3'' test coupon of 0.060' thick IN 625 was
prepared. The coupon was coated with a standard NiCrAlY bond coat
to a thickness of 3-12 mils. Coated iron-based powder and PG-94C
binder was then applied to the coupon to a thickness of about
0.041'' using the procedure set forth above, including the heat
treatment. The iron-based powder included a naturally-formed
aluminum oxide coating. The oxide coating provides electrical
isolation among the particles when higher metal loadings are
desired. After heat treatment, the outer strain of the coating was
measured and found to be about 0.70%.
EXAMPLE 4
[0030] A 3''.times.3'' test coupon of 0.060' thick IN 625 was
prepared. Iron-based powder having a naturally-developed oxide
coating and PG-94C binder was then applied directly to the surface
of the coupon (no bond coat) to a thickness of about 0.041'' using
the procedure set forth above, including the heat treatment. The
coated iron-based powder comprises about 60% by weight of the
sprayed coating, the sprayed coating being a mixture of coated
powder and PG-94C binder. After heat treatment, the outer strain of
the coating was measured and found to be about 0.98%.
[0031] While the invention has been set forth in the examples and
procedure set forth above, the invention is not so limited. The
voltage used in the above examples was limited by the available
test equipment. It is envisioned that higher voltages can be used.
The only limitation on the voltage used is that the equipment and
substrate not be damaged by the applied voltages, such as, for
example, by arc strikes. The available voltages limited the coating
thicknesses tested. It is envisioned that higher voltages can
produce thicker coatings, when so desired.
[0032] The above examples utilized iron-based alloy powders. These
metal powders are readily charged. However, the powders used for
the coating are not so limited, as any powder that can be charged
can be applied by the above described process. The limitation on
the powder is whether the powder can provide the required
protection to the substrate.
[0033] The above binder was Ferro PG-94C. This binder sets forth
the current best mode of practicing the invention. However, other
binders also may be acceptable. The binders must be compatible with
the electrostatic powder spray procedure. The binder utilized was a
glass frit that forms the ceramic matrix of the coating system. It
will be recognized that other binder/matrix materials can be
utilized that will become a part of the final coating. For example,
a silicone may be utilized that can be converted into a glass, a
glassy ceramic or a ceramic, depending upon the heat treatment
applied and intended use. Whether the binder is incorporated into
the final coating or is transitory depends upon the intended use of
the article substrate and the component. Other binders that may be
used include, but are not limited to, GE SR 350, a silicone based
binder, a binder including submicron alumina and smaller particles
such as ALCOA A16SG an active alumina and a high temperature glass
frit, such as V212, available from Vitrifunctions, Inc., Clawson
Ave., Youngwood, Pa. 15697.
[0034] The above described heat treatment is effective for PG-94C
and iron-based powders. It will be understood that this heat
treatment will not be effective to achieve proper adherence of
other types of powders, and other heat treatments will be required
to develop the required properties of another and different powder
or powders as a coating.
[0035] The above examples do not reflect the use of additional
ceramic fillers, However, ceramic fillers that can be applied by
the above spray techniques may also be used as required. In
addition, the size of the powders can be varied to provide required
coating powders. For example, various sized powders can be applied
to provide varying densities. If desired, different powders can be
applied in different layers to achieve different densities.
Furthermore, powders of different compositions can be applied as
distinct layers to achieve different properties in different
layers. These different properties may include different mechanical
properties, different chemical properties, different environmental
properties and different physical properties. However, care must be
taken to provide the proper heat treatments to these layers to
achieve the desired properties. Multiple heat treatments in the
correct sequence may be required. Furthermore, different powders
may be sprayed at the same time into a layer to provide novel
compositions with unique properties. Once again, care must be taken
to provide a proper heat treatment compatible with the powders of
different compositions.
[0036] The present invention can be used for application of
coatings in aircraft engine turbine components that currently are
applied by different processes that have disadvantages or that
cannot readily be applied at all. For example, by mixing different
powders that would otherwise form as a two phase material, and
proper heat treatment, a substantially uniform coating can be
achieved. By proper selection of powder size, for example by
application of metal balls, differences in thermal expansion
between the coating and substrate can be accounted for. Thus, by
properly sizing metal balls, the coating can expand at a different
rate than the underlying substrate to create a strain tolerant
coating. Similarly, different layers can be applied with
differential expansion rates so that the strain due to thermal
expansion can be distributed over the various coating layers to
create a strain-tolerant coating, rather than at an interface
between a coating and a substrate. TBC coatings can also be applied
by the present invention, as it is not limited to metallic balls.
By proper selection of materials and sizing of powders, the density
of TBC coatings produced by current methods can be duplicated as
desired. If desired, the density of these TBC coatings can be
varied to produce a strain-tolerant coating or to vary the thermal
effects as desired by proper application of porosity and cooling
air. Other metals can also be added, such as the family of MCrAlX,
a well-known designation for an expansion matching metal coating
which can also inhibit corrosion, as well as other expansion
matching and/or corrosion inhibiting metal coatings, where M is an
element selected from the group consisting of Fe, Ni Co and
combinations thereof, while X is selected from the group consisting
of Ta, Re and reactive elements, such as Y, Zr, Hf, Si, and grain
boundary strengtheners consisting of B, C and combinations
thereof.
[0037] 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.
* * * * *