U.S. patent application number 13/298326 was filed with the patent office on 2013-05-23 for coating methods and coated articles.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. The applicant listed for this patent is Leonardo Ajdelsztajn, Dennis Michael Gray, James Anthony Ruud. Invention is credited to Leonardo Ajdelsztajn, Dennis Michael Gray, James Anthony Ruud.
Application Number | 20130126773 13/298326 |
Document ID | / |
Family ID | 46888657 |
Filed Date | 2013-05-23 |
United States Patent
Application |
20130126773 |
Kind Code |
A1 |
Ajdelsztajn; Leonardo ; et
al. |
May 23, 2013 |
COATING METHODS AND COATED ARTICLES
Abstract
One aspect of the present invention includes a method. The
method includes combusting a fuel and an oxidant in a combustion
chamber of a thermal spray gun to form a combustion stream. The
method further includes injecting a liquid and a feedstock material
into the combustion stream in the combustion chamber to form an
entrained feedstock stream, wherein the feedstock material includes
a plurality of cermet particles having a median particle size of
less than about 5 microns. The method further includes directing
the entrained feedstock stream on a surface of a substrate to form
a coating, wherein a temperature of the plurality of cermet
particles in the entrained feedstock stream is less than a melting
temperature of the plurality of cermet particles. Coated articles
are also presented.
Inventors: |
Ajdelsztajn; Leonardo;
(Niskayuna, NY) ; Ruud; James Anthony; (Delmar,
NY) ; Gray; Dennis Michael; (Delanson, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ajdelsztajn; Leonardo
Ruud; James Anthony
Gray; Dennis Michael |
Niskayuna
Delmar
Delanson |
NY
NY
NY |
US
US
US |
|
|
Assignee: |
GENERAL ELECTRIC COMPANY
SCHENECTADY
NY
|
Family ID: |
46888657 |
Appl. No.: |
13/298326 |
Filed: |
November 17, 2011 |
Current U.S.
Class: |
251/368 ;
427/455; 427/456; 428/325 |
Current CPC
Class: |
F16K 3/30 20130101; C23C
4/129 20160101; Y10T 428/252 20150115; C09D 1/00 20130101; C23C
24/04 20130101 |
Class at
Publication: |
251/368 ;
427/455; 427/456; 428/325 |
International
Class: |
F16K 25/00 20060101
F16K025/00; B32B 18/00 20060101 B32B018/00; C23C 4/06 20060101
C23C004/06 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH &
DEVELOPMENT
[0001] This invention was made with Government support under
contract number 70NANB7H7009 awarded by the National Institute of
Standards and Technology. The Government has certain rights in the
invention.
Claims
1. A method, comprising: combusting a fuel and an oxidant in a
combustion chamber of a thermal spray gun to form a combustion
stream; injecting a liquid and a feedstock material into the
combustion stream in the combustion chamber to form an entrained
feedstock stream, wherein the feedstock material comprises a
plurality of cermet particles having a median particle size of less
than about 5 microns; and directing the entrained feedstock stream
on a surface of a substrate to form a coating, wherein a
temperature of the plurality of cermet particles in the entrained
feedstock stream is less than a melting temperature of the
plurality of cermet particles.
2. The method of claim 1, wherein maintaining the temperature of
the plurality of cermet particles in the entrained feedstock stream
to be less than the melting temperature of the plurality of cermet
particles is effected substantially by the liquid.
3. The method of claim 1, further comprising injecting the liquid
in an amount sufficient to provide a thermal barrier for the
plurality of cermet particles in the entrained feedstock
stream.
4. The method of claim 1, wherein the temperature of the plurality
of cermet particles in the entrained feedstock stream is maintained
to be less than the melting temperature of the plurality of cermet
particles without the addition of an external coolant.
5. The method of claim 1, wherein a temperature of the plurality of
cermet particles in the entrained feedstock stream is less than
about 0.9 times the melting temperature of the plurality of cermet
particles.
6. The method of claim 1, wherein injecting the liquid and the
feedstock material into the combustion stream comprises injecting a
feedstock mixture comprising the feedstock material disposed in the
liquid through a liquid injection port disposed in the thermal
spray gun.
7. The method of claim 1, wherein the liquid and the feedstock
material are injected into the combustion stream through a coaxial
injection tube port disposed in the thermal spray gun.
8. The method of claim 7, wherein the feedstock material is
injected into the combustion stream through an inner tube of the
coaxial injection port, and the liquid is injected into the
combustion stream through an outer tube of the coaxial injection
port.
9. The method of claim 1, wherein the thermal spray gun comprises a
high velocity air fuel (HVAF) spray gun or a high velocity oxygen
fuel (HVOF) spray gun.
10. The method of claim 1, wherein the liquid comprises water,
alcohol, an organic combustible liquid, an organic incombustible
liquid, or combinations thereof.
11. The method of claim 1 wherein the plurality of cermet particles
comprise a ceramic phase comprising carbides, nitrides, or
combinations thereof.
12. The method of claim 1, wherein the plurality of cermet
particles comprise a metallic phase comprising cobalt, chromium,
nickel, tungsten, or combinations thereof.
13. The method of claim 1, wherein the plurality of cermet
particles are present in the feedstock mixture at a concentration
in a range from about 1 weight percent to about 50 weight percent
of the feedstock mixture.
14. The method of claim 1, wherein the plurality of cermet
particles have a median particle size in a range from about 500
nanometers to about 3 microns.
15. The method of claim 1, wherein the substrate comprises a
component of a steam turbine.
16. The method of claim 1, wherein the substrate comprises a
component of a gate valve.
17. A method, comprising: combusting a fuel and an oxidant in a
combustion chamber of a thermal spray gun to form a combustion
stream; injecting a liquid into the combustion stream in the
combustion chamber through an outer tube of a coaxial injection
port disposed in the thermal spray gun; injecting a feedstock
material into the combustion stream in the combustion chamber
through an inner tube of a coaxial injection port disposed in the
thermal spray gun to form an entrained feedstock stream, wherein
the feedstock comprises a plurality of cermet particles having a
median particle size of less than about 5 microns; and directing
the entrained feedstock stream on a surface of a substrate to form
a coating, wherein a temperature of the plurality of cermet
particles in the entrained feedstock stream is less than a melting
temperature of the plurality of cermet particles.
18. An article, comprising: a substrate and a coating disposed on
the substrate, wherein the coating comprises a plurality of cermet
particles bonded along their prior particle boundaries, wherein the
plurality of cermet particles have a median particle size less than
about 5 microns, and wherein less than 25 percent of the plurality
of cermet particles comprise melted and re-solidified
particles.
19. The article of claim 18, wherein at least 99% of the plurality
of cermet particles have an aspect ratio less than about 5.
20. The article of claim 18, wherein the coating is substantially
free of lamellae.
21. The article of claim 18, wherein the plurality of cermet
particles comprise a ceramic phase comprising carbides, nitrides,
or combinations thereof.
22. The article of claim 18, wherein the plurality of cermet
particles comprise a metallic phase comprising cobalt, chromium,
nickel, tungsten, or combinations thereof.
23. The article of claim 18, wherein a density of the coating is
greater than about 99 percent of the theoretical density.
24. The article of claim 18, wherein the coating is hermetic.
25. The article of claim 18, wherein the coating has a thickness in
a range from about 100 nanometers too about 1000 microns.
26. A gate valve, comprising: a first component; a second
component; and a hermetic coating interposed between the first
component and the second component, wherein the coating comprises a
plurality of cermet particles bonded along their prior particle
boundaries, wherein the plurality of cermet particles have a median
particle size less than about 5 microns, wherein less than 25
percent of the plurality of cermet particles comprise melted and
re-solidified particles.
27. The gate valve of claim 26, wherein the plurality of cermet
particles comprise a ceramic phase comprising carbides, nitrides,
or combinations thereof.
28. The gate valve of claim 26, wherein the plurality of cermet
particles comprise a metallic phase comprising cobalt, chromium,
nickel, tungsten, or combinations thereof.
29. The gate valve of claim 26, wherein the coating is
substantially free of a polymer sealant.
30. The gate valve of claim 26, wherein a density of the coating is
greater than about 99 percent of the theoretical density.
31. The gate valve of claim 26, wherein the first component
comprises a seat and the second component comprises a gate.
Description
BACKGROUND
[0002] The invention generally relates to coating methods and
coated articles. More particularly, the invention relates to
combustion-based thermal spray coating methods and coated
articles.
[0003] Cermet coatings may be used in various components to impart
wear resistance. A thermal spray process may be used to produce
cermet coatings through particle melting or partial melting, and
acceleration of particles onto a substrate. Typical thermal spray
coatings are produced by melting of the particles and
re-solidification on the substrate. In this process, a feedstock
material is heated to an elevated temperature in a spray device and
the heated feedstock material is ejected from the spray device at a
high velocity and thence sprayed against a substrate article
surface. The droplets and particles impact the surface at a high
velocity, and are flattened against the surface to form a
solidified coating having a desired thickness.
[0004] Thermal spray processes often use combustion of fuel with an
oxidizer to provide the heat to the feedstock material. Two
combustion thermal spray processes, high velocity oxygen fuel
(HVOF) and high velocity air fuel (HVAF) techniques, are sometimes
used to form coatings. In each technique, a gas or liquid fuel is
combusted with oxygen (HVOF) or air (HVAF) to produce a high
velocity exhaust stream. A feedstock powder injected into the
exhaust stream is heated and accelerated toward the desired
substrate at sonic or supersonic speeds.
[0005] However, feedstock particles having an average diameter
smaller than about 15-20 microns tend to clog or agglomerate in
conventional HVOF and HVAF equipment, affecting the feeding rate
and the quality of the coating. Further, the HVOF or the HVAF
process, by the nature of combustion process, may produce very high
combustion temperatures that result in high particle temperatures
that could lead to oxidation, decarburization, or dissolution of
the ceramic particles in the metallic binder matrix, which may
affect the properties of the coatings.
[0006] Thus, there is a need for improved methods of depositing
cermet coatings using the thermal spray process. Further, there is
a need for cost-effective coatings having the desired properties
and deposited using the combustion-based thermal spray process.
BRIEF DESCRIPTION OF THE INVENTION
[0007] Embodiments of the present invention are provided to meet
these and other needs. One embodiment is a method. The method
includes combusting a fuel and an oxidant in a combustion chamber
of a thermal spray gun to form a combustion stream. The method
further includes injecting a liquid and a feedstock material into
the combustion stream in the combustion chamber to form an
entrained feedstock stream, wherein the feedstock material includes
a plurality of cermet particles having a median particle size of
less than about 5 microns. The method further includes directing
the entrained feedstock stream on a surface of a substrate to form
a coating, wherein a temperature of the plurality of cermet
particles in the entrained feedstock stream is less than a melting
temperature of the plurality of cermet particles.
[0008] One embodiment is a method. The method includes combusting a
fuel and an oxidant in a combustion chamber of a thermal spray gun
to form a combustion stream. The method further includes injecting
a liquid into the combustion stream in the combustion chamber
through an outer tube of a coaxial injection port disposed in the
thermal spray gun. The method further includes injecting a
feedstock material into the combustion stream in the combustion
chamber through an inner tube of a coaxial injection port disposed
in the thermal spray gun to form an entrained feedstock stream,
wherein the feedstock includes a plurality of cermet particles
having a median particle size of less than about 5 microns. The
method further includes directing the entrained feedstock stream on
a surface of a substrate to form a coating, wherein a temperature
of the plurality of cermet particles in the entrained feedstock
stream is less than a melting temperature of the plurality of
cermet particles.
[0009] One embodiment is an article. The article includes a
substrate and a coating disposed on the substrate, wherein the
coating includes a plurality of cermet particles bonded along their
prior particle boundaries. The plurality of cermet particles have a
median particle size less than about 5 microns and less than 25
percent of the plurality of cermet particles include melted and
re-solidified particles.
[0010] One embodiment is a gate valve. The gate valve includes a
first component; a second component; and a hermetic coating
interposed between the first component and the second component.
The coating includes a plurality of cermet particles bonded along
their prior particle boundaries, wherein the plurality of cermet
particles have a median particle size less than about 5 microns,
and wherein less than 25 percent of the plurality of cermet
particles include melted and re-solidified particles.
DRAWINGS
[0011] These and other features, aspects, and advantages of the
present invention will become better understood when the following
detailed description is read with reference to the accompanying
drawings, wherein:
[0012] FIG. 1 illustrates an apparatus for fabricating a coating
according to an embodiment of the invention.
[0013] FIG. 2 is a flow chart for a method for fabricating a
coating according to an embodiment of the invention.
[0014] FIG. 3 illustrates an apparatus for fabricating a coating
according to an embodiment of the invention.
[0015] FIG. 4 illustrates an article with a coating according to an
embodiment of the invention.
[0016] FIG. 5 illustrates a schematic of an oil and gas gate valve
according to an embodiment of the invention.
[0017] FIG. 6 illustrates cross-sectional scanning electron
micrographs of coatings prepared using liquid injection and powder
injection.
[0018] FIG. 7 illustrates cross-sectional scanning electron
micrographs of various commercially available coatings and coating
prepared using liquid injection.
[0019] FIG. 8 illustrates wear resistance test results of coatings
prepared using liquid injection and powder injection.
[0020] FIG. 9 illustrates wear resistance test results of coatings
prepared using liquid injection and powder injection.
DETAILED DESCRIPTION
[0021] As discussed in detail below, some of the embodiments of the
invention include methods of forming cermet coatings using
combustion-based thermal spray process. Further, some embodiments
of the invention include articles including cermet coatings.
[0022] As noted earlier, typical combustion-based thermal spraying
of cermet coatings may result in decarburization or oxidation of
the cermet particles during the melting and/or partially melting
and re-solidification steps. Further, the morphology and shape of
the deposited cermet particles deposited using the typical
combustion-based thermal spray process may vary from the morphology
and shape of the feedstock particles because of the melting and/or
partial melting and re-solidification of the particles. Thus, it
may be desirable to fabricate coatings using combustion-based
thermal spray process wherein the cermet particles are not
subjected to the melting and re-solidification steps.
[0023] Typical methods of cooling the feedstock particles to
preclude melting include addition of an external coolant, such as,
an inert gas (for example, nitrogen) into the combustion zone
(upstream of the nozzle) or addition of a liquid (for example,
water) into the combustion gases downstream of the nozzle to cool
the combustion gases. However, addition of nitrogen into the
combustion zone may result in formation of impure combustion gases
including water vapor, unreacted hydrocarbon and oxygen. Further,
addition of an external coolant essentially results in cooling of
the combustion gases to temperatures lower than the melting
temperature of the feedstock material, which may affect the
acceleration and impact velocity of the feedstock particles.
[0024] It has been unexpectedly discovered that by injecting the
feedstock and the liquid into the combustion zone (upstream of the
nozzle) of the thermal spray gun, substantial melting of the
particles in the combustion stream may be precluded. Without being
bound by any theory, it is believed that the liquid injected along
with the feedstock into the combustion zone may provide a thermal
barrier to the feedstock particles within the combustion stream and
thus shield the particles from the high temperatures of the
combustion gases in the combustion stream.
[0025] Further, in typical combustion-based thermal spray process,
the coatings include a plurality of lamellae called `splats`,
formed by flattening of the liquid or and/or partially melted
droplets. As the feedstock powder used in typical combustion-based
thermal spray process typically have sizes from 10 micrometers to
above 100 micrometers, the lamellae have thickness in the
micrometer range and lateral dimension from several to hundreds of
micrometers. Between these lamellae, there are often small voids,
such as pores, cracks and regions of incomplete bonding, which may
lead to properties different from bulk materials. Thus, it may be
desirable to form coatings using finer feedstock particles. In
typical thermal spray processes, feedstock powders have been
introduced to the thermal spray flame using gas as the carrier of
the feedstock powders. Fine powder feedstocks, however, are very
difficult to supply at a constant feed rate when gas is used as the
carrier, particularly when their sizes are below 10 micrometers
(.mu.m).
[0026] It has been unexpectedly discovered that manipulating the
feedstock particle size in less than 5 microns range, and by
injecting the feedstock particles along with the liquid into the
combustion zone, enables deposition of coatings that retain
characteristics of the thermally sprayed particles. Without being
bound by any theory, it is further believed that injecting the
feedstock into the combustion zone along with the liquid may
further provide for improved homogeneity of particles and also
allow for greater acceleration of the feedstock particles.
[0027] Embodiments of the present invention include methods for
fabrication of cermet coatings, wherein a substantial portion of
the cermet particles are not subjected to the melting or partial
melting and re-solidification steps. Further, some embodiments of
the present invention include methods for producing fine-grained,
dense, cermet coatings on a substrate using combustion-based
thermal spray process by injecting fine (less than 5 microns)
feedstock particles and a liquid into the combustion stream.
Furthermore some embodiments of the present invention include
articles including fine-grained, dense, cermet coatings, wherein
the coatings include a small amount (less than 25%) of melted and
re-solidified particles.
[0028] Approximating language, as used herein throughout the
specification and claims, may be applied to modify any quantitative
representation that could permissibly vary without resulting in a
change in the basic function to which it is related. Accordingly, a
value modified by a term or terms, such as "about", is not limited
to the precise value specified. In some instances, the
approximating language may correspond to the precision of an
instrument for measuring the value.
[0029] In the following specification and the claims, the singular
forms "a", "an" and "the" include plural referents unless the
context clearly dictates otherwise. As used herein, the term "or"
is not meant to be exclusive and refers to at least one of the
referenced components being present and includes instances in which
a combination of the referenced components may be present, unless
the context clearly dictates otherwise.
[0030] One embodiment includes a method 100 of forming a coating on
a substrate. In one embodiment, the method 100 includes forming a
coating 12 on a surface 15 of a substrate 14 using an apparatus 10,
as shown in FIGS. 1 and 2. FIG. 1 shows a simplified diagram of an
exemplary apparatus 10 including a thermal spray gun 16 for forming
a coating 12 on a substrate 14, according to one embodiment of the
invention. The apparatus 10 may include any suitable spray gun,
including, for example, high velocity air fuel (HVAF) or high
velocity oxygen fuel (HVOF) gun. Although various spray guns are
known in the art and may be used within the scope of various
embodiments of the present invention, the exemplary spray gun 16
shown in FIG. 1 includes a plurality of circumferentially spaced
oxidizer injection ports 18 and fuel injection ports 20 that feed
an oxidant and a fuel (gas or liquid) respectively, to a combustion
chamber 22. The spray gun 16 ignites the fuel/oxidizer mixture in
the combustion chamber 22 that has an inlet side 24 and an outlet
side 26. A combustion zone 28 exists between the inlet side 24 and
the outlet side 26 of the combustion chamber 22. A nozzle 30 is
further disposed in the outlet side 26 of the combustion chamber 22
and the nozzle 30 accelerates the combustion gases generated in the
combustion chamber 22 to high velocities.
[0031] In some embodiments, the method 100 further includes
providing a fuel via the fuel injection port 20 into the combustion
chamber 22. In some embodiments, the method 100 further includes
providing an oxidant via the oxidant injection port 18 into the
combustion chamber 22. The fuel and the oxidant may be injected
into the combustion chamber 22 simultaneously or sequentially.
[0032] Referring to FIGS. 1 and 2, in one embodiment, the method
100 includes, at step 110, combusting a fuel and an oxidant in the
combustion chamber 22 of a thermal spray gun 16 to form a
combustion stream. The term "combustion stream" as used herein
refers to a mixture of gases produced as a result of combustion of
fuel and oxidant in the combustion chamber 22. In some embodiments,
a feedstock material may be transported by the combustion gases of
the combustion stream to form a coating 12 on a surface 15 of the
substrate 14.
[0033] In one embodiment, the oxidant includes oxygen, air, or
combinations thereof. In one embodiment, non-limiting examples of
fuel include a hydrocarbon, a carbonaceous material, an alcohol, or
combinations thereof. In one embodiment, non-limiting specific
examples of the fuel include propylene, propane, methane, butane,
natural gas, hydrogen, kerosene, or combinations thereof.
[0034] In one embodiment, the method 100 further includes providing
a permeable burner block 32 in the combustion zone 28 and
initiating the combustion in the combustion zone after providing
the fuel and the oxidizer to the combustion zone. Referring now to
FIG. 1, the combustion chamber 22 in the thermal spray gun 16
further includes a permeable burner block 32, with an upstream face
31 and downstream face 33, disposed in the combustion chamber 22.
In one embodiment, the permeable burner block 32 is disposed in the
combustion zone 28 of the combustion chamber. In one embodiment,
the permeable burner block 32 includes a plurality of orifices (not
shown) that help in transporting the fuel for efficient combustion
in the combustion zone 28. In one embodiment, the permeable burner
block 32 includes a ceramic material. In one embodiment, the
permeable burner block 32 includes a catalytic plate.
[0035] Without being bound by any theory, it is believed that the
permeable burner block 32 receives the fuel from the fuel injection
port 20 and helps in efficient combustion of the fuel to create
high velocity combustion gases in the combustion stream. Without
being bound by any theory, it is further believed that the high
velocity combustion gases may advantageously provide for lower
temperature combustion gases to heat and accelerate the particles.
Thus, in some embodiments, the high velocity combustion gases
generated via the permeable block 32 may advantageously allow for
bonding of the coating 12 to the substrate 14, without significant
splashing or sputtering.
[0036] Referring again to FIGS. 1 and 2, in one embodiment, the
method 100 further includes, at step 120, injecting a liquid and a
feedstock material into the combustion stream in the combustion
chamber 22 to form an entrained feedstock stream. In some
embodiments, the liquid and the feedstock material are injected
into the combustion zone 28 of the combustion chamber 22 of the
thermal spray gun. In particular embodiments, the liquid and the
feedstock material are injected into the combustion gases of the
combustion stream present in the combustion zone 28 of the thermal
spray gun 16.
[0037] In one embodiment, the liquid is injected into the
combustion chamber 26 via a liquid injection port 34 and the
feedstock material is injected into the combustion chamber 22 via a
feedstock injection port 38, as indicated in FIG. 1. In such
embodiments, the liquid and the feedstock material are co-injected
into the combustion chamber 22 through the liquid injection port 34
and the feedstock injection port 38, respectively.
[0038] As indicated in FIG. 1, in one embodiment, the thermal spray
gun 16 further includes a liquid injection port 34 connected to a
source of liquid 36 and disposed in the combustion chamber through
the inlet side 24. The liquid injection port 34 may be placed
circumferentially, axially or at an oblique angle to the nozzle 30.
In one embodiment, the liquid injection port 34 is placed axially
in the thermal spray gun 16. In another embodiment, as shown in
FIG. 1, the thermal spray gun 16 includes the liquid injection port
34 in the centerline axis of the combustion chamber 22. The liquid
injection port 34 supplies a liquid material that disperses the
feedstock material that gets injected into the stream of combustion
gases in the spray gun 16 to overcome the difficulties experienced
with supplying small-sized particles in conventional coating
apparatus, in some embodiments.
[0039] In one embodiment, the thermal spray gun 16 further includes
a feedstock injection port 38 connected to a feedstock source 40.
The feedstock injection port 38 may be placed circumferentially,
axially or at an oblique angle to the combustion chamber 22. In one
embodiment, as shown in FIG. 1, the thermal spray gun 16 includes a
feedstock injection port 38 disposed axially to the combustion
chamber 22. In one embodiment, the feedstock injection port 38
supplies the feedstock material into the flow of combustion gases.
The combustion gases accelerate the feedstock material and the
feedstock material exits the thermal spray gun 16 to produce the
coating 12 on the substrate 14.
[0040] In another embodiment, the feedstock material is mixed with
the liquid to form a feedstock mixture prior to injecting the
liquid and the feedstock material into the combustion chamber 22.
In some embodiments, the feedstock material may be mixed with the
liquid to form a suspension, a slurry, a colloidal dispersion, a
solution, or combinations thereof. In such embodiments, the thermal
spray gun may only have one injection port, such as, for example,
the liquid injection port 34 for injecting the feedstock and the
liquid into the combustion stream. Further, in such embodiments,
the method 100 includes, at step 120, injecting the liquid and the
feedstock material into the combustion chamber 22 as a feedstock
mixture through the liquid injection port 34.
[0041] Depending, in part, on one or more of the feedstock
material, fuel, temperature of combustion, and the velocity of the
combustion stream, along with other variables, the location of the
tip of the liquid injection port 34 that introduces the liquid or
the feedstock mixture to the combustion stream may vary. In one
embodiment, the liquid injection port 34 may extend up to the
downstream face 33 of the permeable burner block 32. In yet another
embodiment, the liquid injection port 34 may extend through the
combustion zone 28 into the nozzle 30. In a particular embodiment,
as indicated in FIG. 1, the liquid injection port 34 may extend
into the combustion zone 28 between the permeable burner block 32
and the nozzle 30.
[0042] As noted earlier, in particular embodiments, the tip of the
liquid injection port 34 essentially extends upstream of the nozzle
30, such that the liquid or the feedstock mixture is injected into
the combustion stream prior to the discharge of the combustion
stream from the nozzle 30. Similarly, in embodiments including a
separate feedstock injection port 38, the tip of the feedstock
injection port 38 essentially extends upstream of the nozzle 30,
such that the feedstock material is injected into the combustion
stream prior to the discharge of the combustion stream from the
nozzle 30. Without being bound by any theory, it is believed that
injection of the feedstock material and the liquid into the
combustion zone may provide for improved homogeneity of particles
and also allow for greater acceleration of the feedstock
particles.
[0043] In yet another embodiment, the method 100 includes injecting
the liquid and the feedstock into the combustion chamber 22, at
step 120, through a coaxial injection port 66, as indicated in FIG.
3. As shown in FIG. 3, in one embodiment, a coaxial tube injection
port 66 including an inner tube 68 and an outer tube 70 is disposed
in the inlet side of the combustion chamber 22. In one embodiment,
the coaxial injection port 66 is connected to both the source of
feedstock material 62 and the source of liquid 64. In one
embodiment, the inner tube 68 of the coaxial injection port 66 is
connected to the source of liquid 64 and the outer tube 70 is
connected to the source of feedstock material 62. In an alternate
embodiment, the inner tube 68 of the coaxial injection port 66 is
connected to the source of feedstock material 62 and the outer tube
70 is connected to the source of liquid 64.
[0044] In particular embodiments, the method 100 includes, at step
120, injecting the feedstock material into the combustion stream
through the inner tube 68 of the coaxial injection port 66. In some
embodiments, the feedstock material is transported into the
combustion stream along with a carrier, such as, for example, gas
and air, through the inner tube 68 of the coaxial injection port
66. In some embodiments, the method 100 further includes, at step
120, injecting the liquid into the combustion stream through the
outer tube 70 of the coaxial injection port 66. In some
embodiments, the liquid and the feedstock material may be injected
into the combustion stream sequentially. In alternate embodiments,
the liquid and the feedstock material may be injected into the
combustion stream simultaneously.
[0045] In one embodiment, the coaxial injection port 66 may include
a plurality of coaxial tubes to inject the liquid and the feedstock
material into the combustion stream. In one embodiment, the
apparatus 10 may include a plurality of coaxial injection ports 66
to inject the liquid and the feedstock material into the combustion
stream.
[0046] Without being bound by any theory, it is believed that
injection of the liquid along with the feedstock material may
provide thermal shielding of the plurality of the cermet particles
from the hot combustion gases in the combustion stream, in some
embodiments. In some embodiments, the method further includes
injecting the liquid in an amount sufficient to provide a thermal
barrier for the plurality of cermet particles in the entrained
feedstock stream. The amount sufficient to provide the thermal
barrier may be determined by one or more of the cermet material,
the type of fuel, the temperatures generated within the thermal
spray gun, and the design of the thermal spray gun.
[0047] In embodiments including injection of a feedstock mixture
including the liquid and the feedstock material, the plurality of
cermet particles may be present in the feedstock mixture at a
concentration in a range from about 1 weight percent to about 50
weight percent of the feedstock mixture. In some embodiments, the
plurality of cermet particles may be present in the feedstock
mixture at a concentration in a range from about 5 weight percent
to about 25 weight percent of the feedstock mixture.
[0048] Non limiting examples of liquids for injecting into the
combustion stream include water, alcohol, an organic combustible
liquid, an organic incombustible liquid, or combinations thereof.
Specific non-limiting examples of liquids for injecting into the
combustion stream include water, ethanol, methanol, isopropanol,
butanol, hexane, ethylene glycol, glycerol or combinations
thereof.
[0049] As noted earlier, the feedstock material includes a
plurality of cermet particles. The term "cermet" as used herein
refers to a composite material including a ceramic phase and a
metallic phase. Non-limiting examples of suitable metal for use in
the metallic phase of the cermet particles include, but are not
limited to, aluminum (Al), cobalt (Co), nickel (Ni), iron (Fe),
molybdenum (Mo), chromium (Cr), and combinations including at least
one of the foregoing metals. Non-limiting examples of suitable
ceramics for use in the ceramic phase of the cermet particles
include, but are not limited to, carbides such as tungsten carbide
(WC), titanium carbide (TiC), vanadium carbide (VC), chromium
carbide (Cr.sub.3C.sub.2), tantalum carbide (TaC), and silicon
carbide (SiC); nitrides such as aluminum nitride (AlN), silicon
nitride (Si.sub.3N.sub.4), and zirconium nitride (ZrN); borides
such as titanium diboride (TiB.sub.2) and zirconium boride, and
combinations including at least one of the foregoing materials.
[0050] Feedstock materials having different particle sizes may be
used in the methods of making coatings presented herein to form
strong and dense coatings. Without being bound by any theory, it is
believed that use of a liquid carrier and the thermal barrier
effect provided by the liquid may advantageously allow for much
finer feedstock particles than that of the feedstock particles used
in a typical thermal spray method for deposition of coatings.
[0051] In one embodiment, a median particle size of the plurality
of cermet particles is less than about 10 microns. In one
embodiment, a median particle size of the plurality of cermet
particles is less than about 5 microns. In a further embodiment, a
median particle size of the plurality of cermet particles is in a
range from about 100 nanometers to about 5 microns. In a particular
embodiment, a median particle size of the plurality of cermet
particles is in a range from about 500 nanometers to about 3
microns.
[0052] Without being bound by any theory, it is believed that the
introduction of fine particles (less than about 5 microns) may
increase the particle flight velocity, which may reduce the dwell
time in the flame and also allow for fabrication of coatings with
fine particle size. In some embodiments, the reduced median
particle size of the plurality of cermet particles may allow the
method 100 to produce a coating 12 including a plurality of bonded
particles having a median particle size less than about 10 microns.
In some further embodiments, the reduced median particle size of
the plurality of cermet particles may allow the method 100 to
produce a coating 12 including a plurality of bonded particles
having a median particle size less than about 5 microns.
[0053] In one embodiment, as described earlier, a temperature of
the plurality of cermet particles in the entrained feedstock stream
is less than a melting temperature of the plurality of cermet
particles. In a further embodiment, the temperature experienced by
the plurality of cermet particles is less than about 0.9 times a
melting temperature of the plurality of cermet particles. In some
embodiments, the feedstock material is substantially unmelted in
the entrained feedstock stream. In some embodiments, the feedstock
material is substantially unmelted during the step of directing the
feedstock stream on the surface 15 of the substrate to form the
coating 12. The term "substantially unmelted" as used herein means
that less than about 25 percent of the plurality of cermet
particles are unmelted. In some embodiments, less than about 5
percent of the plurality of cermet particles are unmelted.
[0054] In one embodiment, the methods of coating by
combustion-based thermal spray presented here may be different from
the conventional combustion-based thermal spray methods used to
form coatings. As described earlier, a conventional thermal spray
process fabricates the cermet coating through particle melting or
partial melting and accelerating onto a substrate. Further, some
conventional combustion thermal spray methods use an external
coolant to cool the combustion gases such that the gases are cooled
to temperatures lower than the melting point of the particles.
[0055] In contrast, in some embodiments of the methods presented
here, the liquid injected along with the feedstock into the
combustion zone may provide a thermal barrier to the feedstock
particles within the combustion stream and thus shield the
particles from the high temperatures of the combustion stream.
Further, in some embodiments, injection of the feedstock material
and the liquid through the coaxial injection port may allow for
further shielding of the plurality of cermet particles in the
combustion zone by the liquid. Furthermore, in contrast to the
conventional cooling methods of combustion-based thermal spray
process, the combustion gases in the combustion stream may be at
temperatures greater than the melting temperature of the feedstock
particles, and thus have higher velocities.
[0056] In one embodiment, the methods of coating by
combustion-based thermal spray presented here may be different from
the conventional cold spray methods used to form coatings. In
conventional cold spray process, a carrier gas is heated by
external electrical heating and is accelerated by high pressures,
while in some embodiments of the present invention, the carrier gas
is heated by the chemical reaction during combustion and is
accelerated using expansion of the combustion by-product. Further,
in the conventional cold spray process, the carrier gas is
typically maintained below the melting temperature of the
particles. In contrast, in some embodiments of the invention, the
combustion gases are heated above the melting temperature of the
particles, but the liquid injected along with the feedstock
material maintains the temperature of the plurality of cermet
particles below their melting point.
[0057] Without being bound by any theory, it is believed that in
some embodiments, a liquid injected along with the feedstock
material may advantageously enable generation of high velocity, hot
feedstock particles that do not melt and further form dense
coatings including bonded particles. Further, in some embodiments,
the methods as presented here, by precluding melting and
re-solidification of the particles may advantageously reduce
oxidation or decarburization of the cermet particles. Furthermore,
in some embodiments, injection of the feedstock particles along
with the liquid into the combustion zone may advantageously enable
deposition of coatings that retain characteristics (size or shape)
of the feedstock particles.
[0058] As noted earlier, the liquid and the feedstock are injected
into the combustion stream to form an entrained feedstock stream.
In one embodiment, the method 100, further includes, at step 114,
directing the entrained feedstock stream on the surface 15 of the
substrate 14 to form a coating 12 such that at least a part of the
surface 15 of the substrate 12 is covered by the cermet coating 12,
as indicated in FIGS. 1 and 2. In some embodiments, the entrained
feedstock stream is expelled from the spray gun 16 through the
nozzle 30 to form the coating 12. In particular embodiments, the
entrained feedstock stream is sprayed on the surface 15 of the
substrate 14 to form the coating 12.
[0059] In some embodiments, the substrate includes a material
capable of withstanding the conditions of the thermal spray
processes without structural degradation. Non-limiting examples of
the substrate material include plastic, glass, glass ceramic,
metal, metal alloy, ceramic, cermets, semiconductor, or
combinations thereof.
[0060] In one embodiment, the substrate 14 may be pre-heated prior
to the thermal spray process. In one embodiment, the surface 15 of
the substrate 14 may be cleaned to improve adhesion between the
substrate surface and the coating 12. For example, in some
embodiments, the substrate 14 may be cleaned to remove any
impurities such as undesirable oxide formation or presence of
grease.
[0061] In one embodiment, the substrate 14 may be heat treated
after the thermal spray process to form the coating 12. Any
operable heat treatment such as, for example, annealing may be
used. The heat treatment may cause the coating material to
inter-diffuse to some degree with the substrate material.
[0062] In one embodiment, the substrate 14 may be a part of an
apparatus or an article, where an existing coating has degraded and
has to be repaired. In one embodiment, the coating 12 is used to
replace claddings, to provide structural surface layers, or to form
near-net shape components and features on components. The method of
forming a coating, in accordance with embodiments of the present
invention, may be used with a wide variety of compositions and
substrate articles, yielding a variety of different types of
properties. In one example, to build up an article that has been
partially worn away during prior service, the coating 12 may
include the same composition as the substrate article 14. In
another example, to provide a wear-resistant coating at the surface
15, the coating 12 may have a different composition than the
substrate article 14 and may be more wear resistant than the
substrate article 14. In yet another example, to provide a wearing
or abradable coating at the surface 15, the coating may have a
different composition than the substrate article 14 and may be less
wear resistant than the substrate article 14. In a particular
embodiment, the substrate 14 may be a part of an apparatus or an
article including a wear resistant coating.
[0063] In one embodiment of the invention, an article is presented.
The article 80, as shown in FIG. 4, for example, is formed when a
coating 86 is formed on a substrate 82 of the article 80, in
accordance with the method described herein. In one embodiment, the
substrate 82 includes a depositing surface 84. The coating 86 is
formed on the depositing surface 84 of article 80. In one
embodiment, the coating 86 includes a plurality of cermet particles
88 bonded along their prior particle boundaries 90. In one
embodiment, a surface of contact between the coating material 86
and the depositing surface 84 of the substrate 82 is a bondline 92,
as indicated in FIG. 4.
[0064] As noted earlier, in some embodiments, methods of the
present invention may advantageously provide for high-velocity
impact of the cermet particles on the substrate 82 to form a
coating 86 that exhibits one or more of a fine splat size, a fine
grain size, a high density, and a high bond strength to the
underlying surface.
[0065] In one embodiment, the plurality of particles 88 bonded
along their prior particle boundaries 90 in the coating 86 have a
median particle size less than about 10 microns. In one embodiment,
the plurality of particles 88 bonded along their prior particle
boundaries 90 in the coating 86 have a median particle size less
than about 5 microns. In one embodiment, the particles have a
median particle size in a range from about 100 nanometers to about
5 microns. In a particular embodiment, the particles have a median
particle size in a range from about 500 nanometers to about 3
microns.
[0066] Further as noted earlier, the methods of the present
invention advantageously provide for deposition of the coating 86
on the substrate, wherein the plurality of cermet particles are not
subjected to the melting and re-solidification steps that is a
typical of a convention thermal spray process. Accordingly, in one
embodiment, the article 80 includes a coating 86 including a
plurality of cermet particles, wherein less than 25 percent of the
plurality of cermet particles include melted and re-solidified
particles. In one embodiment, the article 80 includes a coating 86
including a plurality of cermet particles, wherein less than 10
percent of the plurality of cermet particles include melted and
re-solidified particles. In one embodiment, the article 80 includes
a coating 86 including a plurality of cermet particles, wherein
less than 5 percent of the plurality of cermet particles include
melted and re-solidified particles. Without being bound by any
theory, it is believed that a coating 86 including a lower amount
of melted and re-solidified particles may provide for improved
properties over conventionally processed coatings.
[0067] Further, in one embodiment, the methods of the present
invention advantageously provide for deposition of a coating 86
that includes substantially non-deformed particles. In some
embodiments, the plurality of bonded particles in the deposited
coating 86 may be further characterized by the lamellae size or the
splat size. The term "lamellae" as used herein refers to molten or
semi-molten particles that have re-solidified in the coating to
form deformed particles. In some embodiments, the term "lamellae"
may be used interchangeably herein with "splat".
[0068] Without being bound by any theory, it is believed that as
the plurality of the particles are not subjected to the melting and
re-solidification steps, the bonded particles in the deposited
coating 86 essentially maintain their original shape and size after
the deposition step. In one embodiment, the plurality of bonded
particles in the deposited coating may be further characterized by
the aspect ratio of the bonded particles in the deposited coating
86. In one embodiment, at least 99% of the plurality of bonded
cermet particles have an aspect ratio less than about 10. In a
further embodiment, at least 99% of the plurality of bonded cermet
particles have an aspect ratio less than about 5. In a particular
embodiment, at least 99% of the plurality of bonded cermet
particles have an aspect ratio in a range from about 1 to about 3.
In some embodiments, low aspect ratio splats may promote stronger
mechanical locking with smooth substrates, precluding the need for
an aggressive surface preparation before thermal spraying. Further,
in some embodiments, smaller splats may also provide smoother
surface finish and denser microstructures in the coating.
[0069] In some embodiments, the coating 86 is substantially free of
lamellae or splats. The term "substantially free" as used in this
context means that less than about 5 percent of the plurality of
bonded particles in the coating 86 include lamellae or splats. In
some embodiments, that less than about 1 percent of the plurality
of bonded particles in the coating 86 include lamellae or
splats.
[0070] In one embodiment, the coating 86 has a density greater than
about 95% of theoretical density of the coating material. In a
further embodiment, the coating 86 has a density greater than about
99% of theoretical density of the coating material. In one
embodiment, the coating 86 has a thickness in a range from about
100 nanometers to about 1000 microns. In a further embodiment, the
coating 86 has a thickness in a range from about 1 micron to about
50 microns.
[0071] In some embodiments, the article 80 may be of any operable
shape, size, and configuration. In some embodiments, the article 80
may include a component of a steam turbine, such as, a seal or a
flange. In some embodiments, the article 80 may include a component
of a steam turbine. In particular embodiments, the article 80 may
include a gate valve used in oil and gas applications.
[0072] In one embodiment of the invention, a gate valve is
presented. In some embodiments, a gate valve suitable for oil wells
for petroleum and natural gas extraction is provided. In particular
embodiments, a gate valve operable to allow or prevent flow of oil
or gas in a subsea tree is presented.
[0073] FIG. 5A shows a schematic drawing of a gate vale for use in
an oil and gas well. FIG. 5B further shows an enlarged view of a
schematic drawing of a gate valve 50, according to one embodiment
of the invention. As indicated in FIG. 5B, in one embodiment, the
gate valve 50 includes a first component 54 and a second component
56. In one embodiment, the first component 54 includes a seat and
the second component includes a gate 56.
[0074] In one embodiment, a hermetic coating 52 is further
interposed between the first component 54 and the second component
56. The term "hermetic coating" as used herein refers to a coating
that has a permeability to helium less than about 1.times.10.sup.-8
atm-cc/s. In one embodiment, the hermetic coating has a
permeability to helium less than about 5.times.10.sup.-9
atm-cc/s.
[0075] In some embodiments, the hermetic coating 12 includes a
plurality of cermet particles bonded along their prior particle
boundaries, as described earlier. In some embodiments, the
plurality of cermet particles have a median particle size less than
about 5 microns. In some embodiments, less than 25 percent of the
plurality of cermet particles include melted and re-solidified
particles, as described earlier. Without being bound by any theory,
it is believed that the use of hermetic coating 12 including a
plurality of bonded cermet particles as described herein may
preclude the need for an additional polymeric sealant that is
typically used in gate valves. In one embodiment, the hermetic
coating 12 is free of a polymer sealant.
EXAMPLES
Example 1
Coarse Powder HVAF Coating Versus Liquid Injection HVAF Coating
Using Fine Particles
Preparation of Coarse Powder HVAF Coating
[0076] Amperit 558.059 Tungsten carbide/cobalt chromium (WC/CoCr)
particles having a d.sub.50 of about 20 microns were employed. The
term "d.sub.50" as used herein means that 50 percent of the
particles have a particle size less than this value. The particles
were fed as dry powder with a carrier gas into a Kermetico AK 07
HVAF thermal spray gun in order to produce a coating on a steel
substrate. Propane fuel was supplied to the gun at 70 psig and air
was supplied at 93 psig. The combustion pressure was adjusted to be
about 55 psi. The gun was operated with a gun traversal speed of
about 1 m/s at a spray distance of 16.25 cm from the substrate. The
deposited coating (Comparative Sample 1) had a thickness of about
300 microns. FIG. 6 shows the cross-sectional scanning electron
microscopy (SEM) images for Comparative Sample 1.
Preparation of Liquid Injection HVAF Coating
[0077] Tungsten carbide/cobalt chromium (WC/CoCr) particles having
a d.sub.50 of about 1.5 microns were combined with water to form a
slurry with 10 wt % solids loading. The slurry was fed into a
Kermetico AK-07 HVAF thermal spray gun. The gun was supplied with
air at 98 psi and propylene at 73 psi to produce a combustion
flame. The gun was rastered across a stainless steel block at 1200
mm/s at a distance of 3 inches to produce a coating (Sample 1)
having a thickness of about 250 microns.
[0078] FIG. 6 shows the cross-sectional scanning electron
microscopy (SEM) images for Comparative Sample 1 and Sample 1. As
indicated in FIG. 6, liquid injection of particles (Sample 1)
results in finer, denser and more uniform microstructure of the
deposited coatings when compared to coatings prepared using coarse
powder injection (Comparative Sample 1). Comparative Sample 1 shows
a plurality of lamellae oriented with the long dimension in the
plane of the coating. In contrast, Sample 1 shows a notable lack of
lamellar features.
Example 2
Commercially Available Cermet Coatings Versus Liquid Injection HVAF
Coating
[0079] Commercial coatings were used as comparative examples.
Comparative Sample 2a is a commercially available
tungsten-carbide-cobalt-chromium coating produced with a detonation
gun process using dry powder with an average particle size greater
than 10 microns [R. J. K. Wood, B. G. Mellor, M. L. Binfield, Wear
Volume 211, (1997) 70-83]. Comparative Sample 2b is a
tungsten-carbide-cobalt-chromium coating produced with JP5000
(Praxair, Inc.) HVOF equipment using dry powder with an average
particle size greater than 10 microns.
[0080] FIG. 7 shows the cross-sectional scanning electron
microscopy (SEM) images for Comparative Samples 2a, 2b, and Sample
1. The resultant SEMs in FIG. 7 showed finer, more uniform and
denser microstructure for Sample 1 when compared to Comparative
Samples 2a and 2b. Comparative Samples 2a and 2b have a plurality
of lamellae with their long dimension oriented in the plane of the
coating. Sample 1 shows a notable lack of lamellar features.
Example 3
Wear Testing of Comparative Samples Versus Liquid Injection HVAF
Coating
[0081] The wear resistance of the coatings (Comparative Sample 1,
Comparative Samples 2a-2b, and Sample 1) were evaluated in a
reciprocating wear test. The coatings were provided on a steel
block and ground to a surface finish of less than 8 micro-inches.
All coatings were tested against a standard wear face in the form
of a coated ring. The wear face was translated linearly in a cyclic
manner with a bearing stress of 25 ksi. The coefficient of friction
was monitored continuously, and failure was determined by a rapid
increase in the coefficient of friction by greater than about 20%
accompanied by a loss of coating material from the block face.
[0082] Comparative Sample 1 failed at 912 cycles. Comparative
Sample 2a failed at 1028 cycles. Comparative Sample 2b failed at
1664 cycles. Sample 1 was tested for 7060 cycles without signs of
failure and the test was stopped. FIGS. 8 and 9 show the wear test
results for Comparative Sample 1 and Sample 1. FIG. 9 shows the
enlarged images of wear test results of Comparative Sample 1 and
Sample 1. As indicated by arrows in FIG. 9, wear tracks in
Comparative Sample 1 show evidence of large pullout of material.
Further, the dark areas in Comparative Sample 1 are deposits of
smeared material from mating surface. In contrast, as indicated by
arrows in FIG. 9, wear tracks in Sample 1 show evidence of
deformation smaller than gridding/lapping marks. Further, Sample 1
did not show evidence of smeared material from the mating surface.
With being bound by any theory, it is believed that the material
that pulled out of the Comparative Sample 1 coating was of the same
size scale as the particles used to deposit the coating and that
the pulled out particles produced the progressive damage that led
to failure. Sample 1, in contrast, was deposited using particles of
a size smaller than the grinding marks, which if pulled out, did
not result in significant wear damage.
Example 4
Helium Permeability Data for Liquid Injection HVAF Coating
[0083] The hermetic capability of liquid HVAF injection coatings
(Sample 1) was tested by measuring the helium permeability. The
samples were tested with a SIMS Helium Leak Detector (S/N: 10335)
using the hard vacuum test port of the device. The metal blocks
test surface were first wiped off with isopropyl alcohol so a
clean, oil free surface existed. An epoxy was then applied to the
KF25 end of a KF25 X KF40 vacuum flange adapter. That flange end
was adhered to the cleaned test block surface. Slight pressure was
applied to the adapter so that the epoxy made hermetic contact with
the test block surface. The epoxy was allowed to cure for a minimum
of 24 hours. Samples were placed on the test port of the detector
and the vacuum cycle initiated. A plastic zip closure type bag was
then placed over the block to fully encapsulate it. 100% helium gas
was introduced inside the bag, and the open bag bottom was clamped
off as much as possible. The test block remained under vacuum on
the detector for a period of 15 minutes. Flow of helium continued
throughout the 15 minute equilibration period. A leak rate reading
from the detector was then recorded.
[0084] The coatings (Sample 1) deposited using liquid HVAF
injection showed helium permeability values lower than about
5.times.10.sup.-9 atm-cc/s, thus indicating desired
hermeticity.
[0085] The appended claims are intended to claim the invention as
broadly as it has been conceived and the examples herein presented
are illustrative of selected embodiments from a manifold of all
possible embodiments. Accordingly, it is the Applicants' intention
that the appended claims are not to be limited by the choice of
examples utilized to illustrate features of the present invention.
As used in the claims, the word "includes" and its grammatical
variants logically also subtend and include phrases of varying and
differing extent such as for example, but not limited thereto,
"consisting essentially of" and "consisting of" Where necessary,
ranges have been supplied; those ranges are inclusive of all
sub-ranges there between. It is to be expected that variations in
these ranges will suggest themselves to a practitioner having
ordinary skill in the art and where not already dedicated to the
public, those variations should where possible be construed to be
covered by the appended claims. It is also anticipated that
advances in science and technology will make equivalents and
substitutions possible that are not now contemplated by reason of
the imprecision of language and these variations should also be
construed where possible to be covered by the appended claims.
* * * * *