U.S. patent application number 12/411632 was filed with the patent office on 2010-09-30 for methods of forming coatings on substrates.
This patent application is currently assigned to HONEYWELL INTERNATIONAL INC.. Invention is credited to Devlin M. Gualtieri, Derek Raybould, George Reimer, Tom Strangman.
Application Number | 20100243464 12/411632 |
Document ID | / |
Family ID | 42543066 |
Filed Date | 2010-09-30 |
United States Patent
Application |
20100243464 |
Kind Code |
A1 |
Gualtieri; Devlin M. ; et
al. |
September 30, 2010 |
METHODS OF FORMING COATINGS ON SUBSTRATES
Abstract
Methods are provided for forming coatings on substrates. In an
embodiment, a method includes forming a first metal layer on the
substrate, the first metal layer comprising a first precious metal,
electrodepositing an active element over the first metal layer to
form an active element layer, the active element selected from the
group consisting of yttrium, scandium, and a lanthanide series
element, applying a second metal layer over the active element
layer, the second metal layer consisting essentially of a metal
selected from a group consisting of a second precious metal,
nickel, and cobalt, heating the substrate including the first metal
layer, the active element layer, and the second metal layer to form
a diffusion-alloyed layer over the substrate, adding aluminum to
the diffusion-alloyed layer, and heating the substrate to diffuse
and react the aluminum with the diffusion-alloyed layer to form a
modified precious metal aluminide coating on the substrate.
Inventors: |
Gualtieri; Devlin M.;
(Ledgewood, NJ) ; Raybould; Derek; (Denville,
NJ) ; Strangman; Tom; (Prescott, AZ) ; Reimer;
George; (Simpsonville, SC) |
Correspondence
Address: |
HONEYWELL/IFL;Patent Services
101 Columbia Road, P.O.Box 2245
Morristown
NJ
07962-2245
US
|
Assignee: |
HONEYWELL INTERNATIONAL
INC.
Morristown
NJ
|
Family ID: |
42543066 |
Appl. No.: |
12/411632 |
Filed: |
March 26, 2009 |
Current U.S.
Class: |
205/181 ;
205/170 |
Current CPC
Class: |
C25D 3/54 20130101; C25D
5/10 20130101; C23C 10/60 20130101; C23C 10/48 20130101; C25D 5/12
20130101; C25D 5/50 20130101; C23C 10/02 20130101; Y02T 50/60
20130101; Y02T 50/67 20130101; C23C 10/52 20130101 |
Class at
Publication: |
205/181 ;
205/170 |
International
Class: |
C25D 5/12 20060101
C25D005/12; C25D 5/10 20060101 C25D005/10 |
Claims
1. A method of forming a coating on a substrate, the method
comprising the steps of: forming a first metal layer on the
substrate, the first metal layer comprising a first precious metal;
electrodepositing an active element over the first metal layer to
form an active element layer, the active element selected from the
group consisting of yttrium, scandium, and a lanthanide series
element; applying a second metal layer over the active element
layer, the second metal layer consisting essentially of a metal
selected from a group consisting of a second precious metal,
nickel, and cobalt; heating the substrate including the first metal
layer, the active element layer, and the second metal layer to form
a diffusion-alloyed layer over the substrate; adding aluminum to
the diffusion-alloyed layer; and heating the substrate to diffuse
the aluminum into the diffusion-alloyed layer to form a modified
precious metal aluminide coating on the substrate.
2. The method of claim 1, wherein the step of forming the first
metal layer comprises depositing platinum onto the substrate.
3. The method of claim 1, wherein the step of forming a first metal
layer comprises electroplating the first metal layer onto the
substrate.
4. The method of claim 1, wherein the step of electrodepositing
comprises: providing a bath comprising a primary alcohol and a
tertiary alcohol, and an electrolyte comprising an yttrium salt;
and electrodepositing yttrium from the yttrium salt onto the first
metal layer.
5. The method of claim 4, wherein the electrolyte comprises yttrium
nitrate.
6. The method of claim 5, wherein the electrolyte comprises
Y(NO.sub.3).3H.sub.2O.
7. The method of claim 1, wherein the step of applying a second
metal layer comprises applying nickel to form the second metal
layer.
8. The method of claim 1, wherein the step of applying a second
metal layer comprises applying cobalt to form the second metal
layer.
9. The method of claim 1, wherein the step of applying a second
metal layer comprises applying platinum to form the second metal
layer.
10. The method of claim 1, wherein the step of applying a second
metal layer comprises electrodepositing nickel onto the active
element layer to form the second metal layer.
11. The method of claim 10, wherein the step of electrodepositing
nickel comprises placing the substrate in an electrolytic bath
including nickel chloride and boric acid.
12. The method of claim 10, wherein the step of electrodepositing
nickel comprises placing the substrate in an electrolytic bath
including nickel fluoroborate, nickel chloride, and boric acid.
13. A method of forming a coating on a substrate, the method
comprising the steps of: forming a platinum layer on the substrate;
electrodepositing yttrium over the platinum layer to form an
yttrium layer; applying a nickel layer over the yttrium layer;
heating the substrate to form a diffusion-alloyed layer over the
substrate, the diffusion-alloyed layer comprising platinum,
yttrium, and nickel; adding aluminum to the diffusion-alloyed
layer; and heating the substrate to diffuse the aluminum into the
diffusion-alloyed layer to form a platinum-yttrium-nickel-aluminide
coating on the substrate.
14. The method of claim 13, wherein the step of electrodepositing
comprises: providing a bath comprising a primary alcohol, a
tertiary alcohol, and an electrolyte comprising an yttrium salt;
and electrodepositing yttrium from the yttrium salt onto the
platinum layer.
15. The method of claim 14, wherein the tertiary alcohol comprises
alpha-terpineol.
16. The method of claim 14, wherein the primary alcohol comprises
ethanol.
17. The method of claim 16, wherein the step of applying the nickel
layer comprises electrodepositing nickel onto the yttrium layer to
form the nickel layer.
18. A method of forming a coating a substrate, the method
comprising the steps of: electrodepositing an active element over
the substrate to form an active element layer, the active element
selected from the group consisting of yttrium, scandium, and a
lanthanide series element; applying a second metal layer over the
active element layer, the second metal layer consisting essentially
of a metal selected from a group consisting of a second precious
metal, nickel, and cobalt; heating the substrate including the
active element layer and the second metal layer to form a
diffusion-alloyed layer over the substrate; adding aluminum to the
diffusion-alloyed layer; and heating the substrate to diffuse the
aluminum into the diffusion-alloyed layer to form a modified
platinum aluminide coating on the substrate.
19. The method of claim 18, further comprising the step of: forming
a first metal layer on the substrate, before the step of
electrodepositing, the first metal layer comprising nickel or
cobalt.
20. The method of claim 18, wherein the step of electrodepositing
comprises: providing a bath comprising a primary alcohol, a
tertiary alcohol, and an electrolyte comprising an yttrium salt;
and electrodepositing yttrium from the yttrium salt onto the
substrate.
Description
TECHNICAL FIELD
[0001] The inventive subject matter generally relates to
substrates, and more particularly relates to coatings formed on
substrates.
BACKGROUND
[0002] Turbine engines are used as the primary power source for
various kinds of aircraft. The engines may also serve as auxiliary
power sources that drive air compressors, hydraulic pumps, and
industrial electrical power generators. Most turbine engines
generally follow the same basic power generation procedure.
Compressed air is mixed with fuel and burned, and the expanding hot
combustion gases are directed against stationary turbine vanes in
the engine. The vanes turn the high velocity gas flow partially
sideways to impinge onto turbine blades mounted on a rotatable
turbine disk. The force of the impinging gas causes the turbine
disk to spin at high speed. Jet propulsion engines use the power
created by the rotating turbine disk to draw more air into the
engine, and the high velocity combustion gas is passed out of the
gas turbine aft end to create forward thrust. Other engines use
this power to turn one or more propellers, electrical generators,
or other devices.
[0003] Because fuel efficiency increases as engine operating
temperatures increase, turbine engine blades and vanes are
typically fabricated from high-temperature materials such as
nickel-based superalloys. However, although nickel-based
superalloys have good high-temperature properties and many other
advantages, they may be susceptible to corrosion, oxidation,
thermal fatigue, and/or foreign particle impact when exposed to
harsh working environments during turbine engine operation. As a
result, diverse coatings and coating methods have been developed to
increase the operating temperature limits and service lives of the
high pressure turbine components, including the turbine blade and
vane airfoils.
[0004] One category of conventional airfoil coatings includes
platinum aluminide coatings. Platinum aluminide coatings may serve
as bond coats, which work in conjunction with thermal barrier
coatings to protect the turbine component. However, oxygen may
permeate the porous thermal barrier coating and may react with
aluminum from the platinum aluminide coating to form an
interfacial, protective aluminum oxide (alumina) scale over the
platinum aluminide coating. Adhesion of the thermal barrier coating
to the component is dependent upon the adhesion of the interfacial
alumina scale to the platinum aluminide coating. In some cases, in
order to enhance alumina scale adhesion, the platinum aluminide
coating may be modified with the addition of oxygen active elements
such as silicon, hafnium, and yttrium.
[0005] Although the aforementioned formulations are sufficient for
enhancing adhesion of the alumina to the platinum aluminide
coating, processes by which the formulations coatings are formed
may be improved. For example, because the oxygen active elements
such as yttrium readily react with air at room temperature,
conventional processes such as electron beam-physical vapor
deposition (EB-PVD) and plasma spraying are typically used to
deposit prealloyed materials containing yttrium as an alloying
element to form the coating. However, the prealloyed materials are
costly and the associated deposition processes for prealloyed
materials are relatively expensive to perform. Moreover, if a thin
layer of unalloyed yttrium were to be deposited on the turbine
component in elemental form, the unalloyed yttrium would be
susceptible to rapid oxidation and would form yttrium oxide.
Inclusion of a layer of yttrium oxide into the platinum aluminide
coating could disrupt the coating's ability to form an adherent
protective alumina scale.
[0006] Accordingly, it is desirable to have an active element
modified platinum aluminide coating that is improved over
conventional platinum aluminide coatings. Alternatively, it is
desirable to have active element modified nickel aluminide and
cobalt aluminide coatings that perform comparably to higher cost
conventional platinum aluminide coatings. More particularly, it is
desirable to have a platinum aluminide coating that may be more
corrosion-resistant and/or oxidation-resistant than conventional
platinum aluminide coating. In addition, it is desirable to provide
methods of forming nickel aluminide, cobalt aluminide, and platinum
aluminide coatings that are less time-consuming, less expensive,
and relatively simple to perform as compared to conventional
formation methods. Furthermore, other desirable features and
characteristics of the inventive subject matter will become
apparent from the subsequent detailed description of the inventive
subject matter and the appended claims, taken in conjunction with
the accompanying drawings and this background of the inventive
subject matter.
BRIEF SUMMARY
[0007] Methods of forming coatings are provided.
[0008] In an embodiment, and by way of example only, a method
includes forming a first metal layer on the substrate, the first
metal layer comprising a first precious metal, electrodepositing an
active element over the first metal layer to form an active element
layer, the active element selected from the group consisting of
yttrium, scandium, and a lanthanide series element, applying a
second metal layer over the active element layer, the second metal
layer consisting essentially of a metal selected from a group
consisting of a second precious metal, nickel, and cobalt, heating
the substrate including the first metal layer, the active element
layer, and the second metal layer to form a diffusion-alloyed layer
over the substrate, adding aluminum to the diffusion-alloyed layer,
and heating the substrate to diffuse and react the aluminum with
the diffusion-alloyed layer to form a modified precious metal
aluminide coating on the substrate.
[0009] In another embodiment, by way of example only, a method
includes forming a platinum layer on the substrate,
electrodepositing yttrium over the platinum layer to form an
yttrium layer, applying a nickel layer over the yttrium layer,
heating the substrate to form a diffusion-alloyed layer over the
substrate, the diffusion-alloyed layer comprising platinum,
yttrium, and nickel, adding aluminum to the diffusion-alloyed
layer, and heating the substrate to diffuse and react the aluminum
with the diffusion-alloyed layer to form a
platinum-yttrium-nickel-aluminide coating on the substrate.
[0010] In another embodiment, by way of example only, a method
includes forming a nickel layer on the substrate, electrodepositing
yttrium over the nickel layer to form an yttrium layer, applying a
nickel layer over the yttrium layer, heating the substrate to form
a diffusion-alloyed layer over the substrate, the diffusion-alloyed
layer comprising yttrium and nickel, adding aluminum to the
diffusion-alloyed layer, and heating the substrate to diffuse and
react the aluminum with the diffusion-alloyed layer to form a
nickel-yttrium-aluminide coating on the substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The inventive subject matter will hereinafter be described
in conjunction with the following drawing figures, wherein like
numerals denote like elements, and
[0012] FIG. 1 is a cross section of a portion of a component,
according to an embodiment; and
[0013] FIG. 2 is a flow diagram of a method for forming a coating
on a component, according to an embodiment.
DETAILED DESCRIPTION
[0014] The following detailed description is merely exemplary in
nature and is not intended to limit the inventive subject matter or
the application and uses of the inventive subject matter.
Furthermore, there is no intention to be bound by any theory
presented in the preceding background or the following detailed
description.
[0015] FIG. 1 is a cross section of a portion of a component 100,
according to an embodiment. The component 100 is configured to be
oxidation and hot corrosion resistant when used in high temperature
applications (e.g., a component operating in an oxidizing
environment and having metal temperatures up to about 1150.degree.
C.). For example, the component 100 may be a turbine engine
component, such as a turbine blade, stator, and the like. The
component 100 includes a substrate 102, a first coating 104, and a
second coating 106, in an embodiment. The substrate 102 may
comprise a metal, a metallic alloy or a metallic superalloy, such
as a nickel-base, cobalt-base, or iron-base alloy or superalloy. In
other embodiments, the substrate 102 may comprise other
materials.
[0016] The first coating 104 may serve as a bond coat and is
adapted to cooperate with the second coating 106 to protect the
substrate 102, and hence, the component 100, from high gas
temperatures and/or oxidation, in an embodiment. In an embodiment,
the first coating 104 may have a thickness in a range of from about
25 .mu.m to about 300 .mu.m. In another embodiment, the first
coating 104 may have a thickness in the range of 25 to 75 .mu.m. In
another embodiment, the thickness of the first coating 104 may be
greater or less than the aforementioned range. According to an
embodiment, the first coating 104 may comprise a precious metal,
nickel or cobalt, an active element, a protective metal, and
aluminum. In an embodiment, the term "precious metal" may be
defined herein as an element selected from the group containing
rhodium, palladium, iridium and platinum. In accordance with an
embodiment, the precious metal comprises platinum. In a lower-cost
embodiment, the precious metal may be replaced with nickel or
cobalt. The term "active element" may be defined as an element that
improves oxidation resistance of the alloy of the first coating 104
by enhancing oxide scale adhesion and acting as a sulfur getter
(e.g., an element having an affinity to sulfur). In an example, the
active element may be deposited in its metallic form and then
alloyed with other constituents of the coating by heat treatment.
According to an embodiment, the active element may comprise
yttrium. In another embodiment, the active element may comprise
scandium. In still another embodiment, the active element may
comprise a lanthanide series element, such as an element having an
atomic number between 57 and 71. The term "protective metal" as
used herein may refer to a metal that may be selected to protect
the active element from oxidation prior to the vacuum or inert gas
heat treatment that alloys the active element with the precious
metal and protective metal layers during formation of the first
coating 104. In an embodiment in which the active element comprises
yttrium, the protective element may comprise an element such as
nickel or cobalt. Alternatively, the precious metal may serve as
the protective element. In another embodiment, another precious
metal may be included in the alloy of the first coating 104 and may
serve as the protective element.
[0017] In accordance with an embodiment, the first coating 104 may
comprise a modified platinum aluminide coating. The first coating
104 may have a composition including platinum, yttrium, nickel, and
aluminum, in an embodiment. In another embodiment, the first
coating 104 may comprise a composition including platinum, yttrium,
cobalt, and aluminum. In still another embodiment, the first
coating 104 may comprise a composition including platinum, yttrium,
palladium, and aluminum. In a lower-cost embodiment, the first
coating may comprise nickel, cobalt, yttrium, and aluminum but
contain no precious metal. In still other embodiments, the first
coating 104 may comprise any other combination of elements provided
above in the description relating to the first coating 104.
[0018] According to an embodiment, when the first coating 104
comprises Pt, Y, and Ni and has been diffusion heat treated and
aluminized, the Pt, Ni, Y, and Al constituents of the coating may
be partitioned into gamma Ni, gamma prime Ni.sub.3Al, and beta NiAl
phases, which are solid solutions. Yttrium may also be present as a
nickel-yttride intermetallic phase. According to another
embodiment, when the first coating 104 comprises Pt, Y, and Co and
has been diffusion heat treated and aluminized, the Pt, Co, Y, and
Al constituents of the coatings may be partitioned into gamma Co
and beta CoAl phases, which are solid solutions. Yttrium may also
be present as a cobalt-yttride intermetallic phase. In any case,
the preferred amount of yttrium in coating 104 is in the range of
about 0.01% to about 0.6% by weight, in an embodiment. However, in
other embodiments, the amount of yttrium may be greater or less
than the aforementioned range.
[0019] No matter the particular elements present in the first
coating 104, the first coating 104 is formed such that some of the
constituents of the alloy may not be substantially evenly
distributed throughout the first coating 104. For example, the
presence of the alloy constituents in the first coating 104 may be
graded. In another example, in order to improve oxidation
resistance of the first coating 104, the active element may be
diffused such that a higher concentration of active element is
found in a first area of the first coating 104 that is adjacent to
the substrate 102 than in a second area of the first coating 104
that is adjacent to the second coating 106. In still another
embodiment, aluminum may be diffused such that a higher
concentration thereof is found in the second area of the first
coating 104 than in the first area of the first coating 104.
[0020] An optional second coating 106 is formed over the first
coating 104 and is formulated to provide the component 100 with
improved thermal resistance. According to an embodiment, the second
coating 106 may serve as a thermal barrier coating. In this regard,
the second coating 106 may comprise a ceramic, such as stabilized
tetragonal and cubic zirconia and stabilized tetragonal and cubic
hafnia, and mixtures thereof. In another embodiment, the second
coating 106 may comprise about 7 weight % yttria-stabilized
tetragonal zirconia. In still other embodiments, other suitable
materials for use as thermal barrier coatings may alternatively be
employed. In an embodiment, the second coating 106 may have a
thickness in a range of from about 50 .mu.m to about 250 .mu.m. In
another embodiment, the thickness of the second coating 106 may be
greater or less than the aforementioned range.
[0021] During deposition of the second coating 106 (e.g., thermal
barrier coating) and during subsequent service, an alumina layer
108 may thermally grow at the interface between coatings 104 and
106. According to an embodiment, the alumina layer 108 may have an
initial thickness in a range of from about 0.1 .mu.m to about 2.0
.mu.m. In another embodiment, the thickness of the alumina layer
108 may be greater or less than the aforementioned range.
[0022] FIG. 2 is a flow diagram of a method 200 for forming
coatings on a component, such as coatings 104, 106 on component
100, according to an embodiment. In an embodiment, the method 200
includes forming a first metal layer on a substrate, step 202. The
first metal layer may comprise nickel, cobalt, or a first precious
metal, which may be selected from the constituents noted above as
described in relation to the first coating 104 (FIG. 1). In any
case, the first metal layer may be electroplated over the
substrate, in an embodiment. In another embodiment other deposition
methods, including chemical and/or physical vapor deposition, may
alternatively be employed. The first metal layer may be deposited
to a thickness in a range of from about 3 .mu.m to about 15 .mu.m,
in an embodiment. In another embodiment, the thickness of the first
metal layer may be greater or less than the aforementioned range.
In another embodiment, if the substrate may be directly
electroplated with an active element, the first metal layer is
optional.
[0023] Next, an active element is electrodeposited over the first
metal layer to form an active element layer, step 204. In an
embodiment, the active element includes yttrium. In another
embodiment, the active element may comprise scandium. In still
another embodiment, the active element may comprise a lanthanide
series element, such as an element having an atomic number between
57 and 71. However, in other embodiments, other active elements,
such as those described above in conjunction with the first coating
104, alternatively may be employed. To form the active element
layer, a first electrolytic bath may be prepared. In an embodiment,
the first electrolytic bath includes a solvent and an electrolyte
solute. In accordance with an embodiment, the first electrolytic
bath may be substantially or entirely non-aqueous and may include a
solvent that consists of a mixture of a primary and a tertiary
alcohol. Primary alcohols that may be included in the first
electrolyte bath include methanol and ethanol, in an embodiment.
According to another embodiment, pure ethanol as a primary alcohol,
may be included. In still another embodiment, denatured ethanol
that includes some methanol (e.g. about 5% methanol) may be
employed as the primary alcohol. In another embodiment, a suitable
tertiary alcohol for inclusion in the solvent may comprise alpha
terpineol. In an example, the tertiary alcohol may be included at a
concentration in a range of from about 20 and about 80 percent of a
total volume of the solvent, with a substantial remainder of the
total solvent weight being the primary alcohol. An electrolyte
solvent may include a tertiary alcohol and a primary alcohol at
about a 1:1 volume ratio.
[0024] The first electrolyte solute in the bath includes a salt of
the active element to be electro-deposited onto the substrate.
Metal nitrates are one class of electrolyte solutes, and are
particularly effective when yttrium is the active metal to be
electro-deposited. In an embodiment, the electrolyte solute
includes Y(NO.sub.3).3H.sub.2O, which is a dehydration product
obtainable by roasting Y(NO.sub.3).6H.sub.2O at a suitable
temperature (e.g. 100.degree. C.) to remove three waters of
hydration. The electrolyte solute may be included in the bath
solution at least at a 10 milliMolar (mM) concentration, and
preferably at least at a 100 mM concentration, and more preferably
at least at a 200 mM concentration.
[0025] A buffer may also be included in the first electrolyte bath
as necessary. In an embodiment, the buffer may include sodium
acetate. Because sodium acetate is commonly obtained in a hydrated
form, typically with three waters of hydration per molecule of
sodium acetate, it may be dehydrated by heating above 123.degree.
C. to form anhydrous sodium acetate before being added to the
electrolytic bath. Sodium acetate may be included in the bath at a
5 to 20 mM concentration, and is preferably included at about a 10
mM concentration.
[0026] At some point prior to deposition, the first metal layer or
other surfaces of the component may be cleaned using a cleaning
solvent such as methanol, in an embodiment. In another embodiment,
the component additionally or alternatively may be prepared by
masking areas on which a coating is undesirable using a masking
material that is compatible with the electrolytic bath.
[0027] In order to prevent oxidation of the component surface, or
oxidation of the active element being electrodeposited onto the
surface, the bath is placed in a controlled and substantially
oxygen-free environment during the electrodeposition process. For
example, an inert gas may be blown over the bath, or the bath may
be placed into a chamber of the inert gas. Suitable inert gases
include dry nitrogen and argon. According to an embodiment,
electrodeposition may be performed at an ambient temperature
ranging from about 0.degree. C. to about 50.degree. C., or from
about 20 to about 25.degree. C.
[0028] Electrical parameters for electrodeposition of the active
element onto the component substrate may be adjusted depending on
factors such as the desired coating thickness and the substrate
composition. According to an embodiment, platinum plates may be
used and a current of about 2.5 milliamperes (mA) per square inch
of component surface area to be coated is applied to the plates.
The current may be maintained for between about an hour to five
hours, in an embodiment. In other embodiments, the current may be
maintained for a longer or shorter duration. For example, in
embodiments in which a thinner layer may be desired, the current
may be maintained for about 1.5 hours. In embodiments in which a
thicker layer may be desired, the current may be maintained for
about 3 hours. To form a modified platinum aluminide coating having
a thickness of about 50 .mu.m, the active element is
electrodeposited to a thickness ranging between about 0.4 and about
1.0 .mu.m to obtain a finalized coating having between about 0.2
and about 0.6 weight percent yttrium.
[0029] After electrodepositing the active element, a second metal
layer is applied over the active element layer, step 206. The
second metal layer is formulated to protect the active element from
oxidation before subsequent heat treatment occurs. By protecting
the active element, the active element may diffusion-alloy with the
first and second metal layers, and in some cases, with the adjacent
substrate. The second metal layer may consist essentially of one or
more metals selected from those described above in conjunction with
protective elements. In general, the protective element may be
selected from a group consisting of a second precious metal,
nickel, and cobalt. The second precious metal may be substantially
identical to the precious metal deposited for the first metal
layer, in an embodiment. In another embodiment, the second precious
metal may be different from the precious metal comprising the first
metal layer.
[0030] In any case, the second metal layer may be formed using
electrodeposition. In accordance with an embodiment in which the
second metal layer comprises nickel and electrodeposition is
employed, the second metal layer may be deposited via a second
electrolytic bath including a solvent and an electrolyte solute. In
accordance with an embodiment, the solvent includes distilled
water. In another embodiment, the solvent includes a solute
component and a buffer component. For example, the solvent may
comprise a solute component of nickel chloride (NiCl.sub.2) and a
buffer component of boric acid (H.sub.3BO.sub.3). According to an
embodiment, the nickel chloride may be present in a molarity of
about one, and the boric acid is present in a molarity of about
0.5. In another embodiment, the solvent comprise solute components
of nickel fluoroborate (Ni(BF.sub.4).sub.2 and nickel chloride
(NiCl.sub.2), and a buffer component is boric acid
(H.sub.3BO.sub.3). The nickel fluoroborate may be present in a
molarity of about three-quarters, the nickel chloride is present in
a molarity of about 0.02, and the boric acid is present in a
molarity of about a third, in an embodiment. Depending on the
particular material for use in the second metal layer, salts, such
as nickel fluoride, nickel chloride, cobalt nitrate, cobalt
sulfate, or cobalt methanesulfonate may be employed. Generally,
sulfur-containing solutes should be avoided in preparation of
coatings for high temperature corrosion resistance.
[0031] At some point prior to deposition, the second metal layer or
other surfaces of the component may be cleaned using a cleaning
solvent such as methanol or denatured ethanol, in an embodiment. In
another embodiment, the component additionally or alternatively may
be prepared by masking areas on which a coating is undesirable
using a masking material that will not substantially degrade in the
second electrolytic bath.
[0032] The second electrolytic bath may be placed in a controlled
and substantially oxygen-free environment during the
electrodeposition process. For example, an inert gas may be blown
over the bath, or the bath may be placed into a chamber of the
inert gas. Suitable inert gases include dry nitrogen and argon.
According to an embodiment, electrodeposition may be performed at
an ambient temperature ranging from about 0.degree. C. to about
50.degree. C., or from about 20.degree. C. to about 25.degree.
C.
[0033] Electrical parameters for electrodeposition of the second
layer material onto the active element layer may be adjusted
depending on factors such as the desired coating thickness and the
substrate composition. According to an embodiment, nickel anode
plates may be placed in the second electrolytic bath. To further
prevent oxidation of the active element layer before immersion into
the second electrolytic bath, an electric potential may be applied
between substrate and the plates. In any case, after the plates and
substrate are placed in the bath, a current of about 2.5
milliamperes (mA) per square inch of component surface area to be
coated may be applied to the plates. The current may be maintained
for between about an hour to five hours, in an embodiment. In other
embodiments, the current may be maintained for a longer or shorter
duration. For example, in embodiments in which a thinner layer may
be desired, the current may be maintained for about 1.5 hours. In
embodiments in which a thicker layer may be desired, the current
may be maintained for about 3 hours. The second metal layer may be
electrodeposited to a thickness ranging between about 1.0 and about
20.0 .mu.m. In other embodiments, the second metal layer may have a
greater thickness.
[0034] Next, the substrate including the first metal layer, the
active element layer, and the second metal layer are heated to form
a diffusion-alloyed layer over the substrate, step 208. In an
embodiment, a suitable temperature is selected to thermally diffuse
the active element into the first and second metal layers to form a
modified metal layer. Additionally, thermal diffusion may be
performed under vacuum in order to remove oxygen from the
environment. For coatings applied to superalloy substrates,
diffusion of the coating may be in the temperature range of
1000.degree. C. to 1150.degree. C. According to one embodiment,
thermal diffusion-alloying of yttrium, platinum, and nickel is
performed in a vacuum by maintaining a temperature of about
1037.degree. C. for a duration in a range of from about one hour to
about three hours.
[0035] After the diffusion-alloying of the platinum, yttrium and
nickel layers has been completed, aluminum may be added to the
coating, step 210. The aluminum may be added using one of numerous
methods. For example, aluminum may be added by a chemical vapor
deposition process that both deposits aluminum and reacts it with
the other elements in the coating to form aluminum-rich
intermetallic phases. Alternatively, elemental aluminum may be
deposited onto the surface of the coating by various deposition
methods, including low temperature chemical vapor deposition and
physical vapor deposition. The substrate is heated to form the
first coating, step 212. In an embodiment, heat treatment is
performed and the elemental aluminum reacts and alloys the aluminum
with the other constituents of the coating. The diffusion heat
treatment may be performed in the range of 900.degree. C. to 1100
C. According to one exemplary method, thermal diffusion of aluminum
into the modified platinum layer is performed in a vacuum by
maintaining a temperature of about 1060.degree. C. for a duration
in a range of from about one hour to about five hours, preferably
four hours.
[0036] A second coating may be formed over the first coating, step
214. In accordance with an embodiment, the second coating may be a
thermal barrier coating. To improve adhesion of the second coating
to the first coating, a metastable alumina layer may be formed over
the first coating. In an embodiment, a thin layer (for example,
having a thickness in the range of from about 0.1 to about 5 .mu.m,
and typically of less than 1 .mu.m) of metastable alumina may be
applied by various deposition processes known in the art. As
non-limiting examples, metastable alumina layer may be applied by a
sol gel process, by a physical vapor deposition process, or by a
chemical vapor deposition (CVD) process, such as atomic layer
deposition.
[0037] Following application of metastable alumina layer, if
employed, the second coating may be applied. In accordance with an
embodiment, the second coating may comprise a material suitable for
the thermal barrier coating, such as a ceramic that can adhere to
alumina. In an embodiment, the ceramic may be stabilized tetragonal
or cubic phase zirconia or hafnia. In another embodiment, the
ceramic may be yttria-stabilized zirconia (YSZ). The second coating
may be applied by a deposition process, such as by electron beam
evaporation-physical vapor deposition (EB-PVD), plasma spraying,
cold-spraying, chemical vapor deposition or another suitable
deposition or application process. According to an embodiment, the
substrate is then heated to a temperature from about 1000.degree.
C. to about 1150.degree. C. Heat treatment may be carried out in an
inert atmosphere, such as argon, or in a vacuum and may be
continued until the metastable alumina layer, if employed, is fully
transformed to comprise crystallographically stable alpha alumina
that contains a dispersion of particles solubilized from the second
coating. For example, in a case where YSZ is used, the
transformation of metastable alumina layer to stable phases may
comprise a mixture of alpha alumina, yttrium aluminum garnet (YAG),
and zirconia. The presence of the mixed alpha alumina and zirconia
may improve cohesion between the interfacial alumina layer and the
second coating.
[0038] The following example demonstrates various embodiments of
the coatings and methods of forming coatings on substrates. These
examples should not be construed as in any way limiting the scope
of the inventive subject matter.
Example
[0039] Y(NO.sub.3).sub.3.3H.sub.2O was prepared by roasting
Y(NO.sub.3).sub.3.6H.sub.2O above 100.degree. C. Anhydrous sodium
acetate was prepared by roasting CH.sub.3COONa.3H.sub.2O above
123.degree. C. to form CH.sub.3COONa. An electrolytic bath was
prepared by adding 41.238 grams of Y(NO.sub.3)3.3H.sub.2O and
0.6152 grams of NaC.sub.2H.sub.3O.sub.2 to a mixture of 375 mL
denatured ethanol (95% ethanol, 5% methanol) and 375 mL of
alpha-terpineol. This electrolytic bath was maintained at a
temperature of 50.degree. C. in a closed vessel for four hours to
ensure solution of the solid constituents. The electrolytic bath
was then cooled to room temperature.
[0040] A button of superalloy SC-180, 2.54 centimeters (cm) (1
inch) in diameter and 0.32 cm (one-eighth inch) thickness was
attached by welding to an electrically conducting wire and
electroplated with a thin (about 5 microns) layer of platinum.
After removal from the platinum electroplating bath, the button was
rinsed and dried. The button was subsequently placed in the center
of the region between two parallel platinum plates, 5.08
cm.times.11.43 cm (2 inch by 4.5 inch) rectangular dimension,
separated by a 3.81 cm (1.5 inch) spacing. The approximate surface
area of the button is 12.67 square centimeters (1.96 square
inches). This assembly and the electroplating solution were placed
in an atmosphere-controlled chamber of dry nitrogen gas. The
assembly was then placed into the yttrium plating solution, a
current source was connected such that the negative lead was
attached to the button, and the positive lead was attached to both
platinum plates.
[0041] A current of 25 milliamperes was allowed to flow between the
two platinum plates and the button for a period of 30 minutes. A
gentle stirring was applied to the solution during electroplating
by a one-inch square Teflon stirrer rotated in-plane at about 100
revolutions per minute. A voltage of about four volts was required
to maintain the current flow in the electroplating cell. A total
charge transfer of 4.5 Coulombs was obtained from a flow of 2.5
milliamperes for 30 minutes, corresponding to a plated yttrium
layer of about 0.25 micrometer (.mu.m) thickness on the surface of
the button, assuming perfect efficiency in the plating process.
[0042] After electroplating, the excess solution was washed from
the button in a denatured ethanol bath, and the button was allowed
to dry in the controlled oxygen-free atmosphere. Previously placed
in the controlled atmosphere chamber was a nickel electroplating
solution prepared by dissolving 187.5 grams of nickel chloride and
22.5 grams of boric acid in 750 mL of water. The yttrium plated
button was placed in an electroplating vessel of the same geometry
as the one for yttrium plating, except that nickel electrodes were
used in place of platinum. To prevent reaction of the yttrium with
the water solution, a potential was applied between the button and
the nickel electrode before immersion into the nickel plating bath.
The polarity of the button was negative with respect to the nickel
electrodes. Application of a current of 125 mA for 22.5 minutes
resulted in a nickel coating of about 2.5 micrometers over the
existing yttrium coating. X-ray fluorescence analysis of a similar
button viewed in cross-section in a scanning electron microscope
showed the expected presence of the elemental metals in the
expected thicknesses.
[0043] After exposure to atmosphere, the superalloy button with
layers of platinum, yttrium and nickel deposited in succession, was
placed into a vacuum furnace and heated at 1037.degree. C.
(1900.degree. F.) for three hours to allow diffusion-alloying of
the superalloy surface with the platinum, yttrium and nickel
layers. The furnace was then allowed to cool to room temperature
over the course of several hours, and the button was removed from
the furnace. The button was then placed in another vacuum chamber,
and an additional layer of aluminum was deposited onto the button
by evaporation and condensation of aluminum onto the surface of the
button. The button was then heat treated in another vacuum furnace
for diffusion and reaction of the aluminum to create a superalloy
button with a platinum-yttrium-nickel-aluminide coating that
comprised aluminum rich intermetallic phases. This coated button
was inspected and showed improved lifetime in an accelerated
cyclic-oxidation test at 1149.degree. C. (2100.degree. F.) over
buttons with a platinum-aluminide coating without the yttrium and
nickel additions.
[0044] Active element modified platinum aluminide coatings have
been provided that are improved over conventional platinum
aluminide coatings. More particularly, because the platinum
aluminide coatings include both yttrium and nickel and are formed
according to the methods described above, they may be more
corrosion-resistant and/or oxidation-resistant than conventional
platinum aluminide coatings. Improved oxide scale adhesion on these
active element modified Pt-aluminide coatings also enable thermal
barrier coatings with improved spalling lives. The above-described
methods of forming the modified platinum aluminide coatings may be
less time-consuming, less expensive, and relatively simpler to
perform as compared to conventional formation methods.
[0045] While at least one exemplary embodiment has been presented
in the foregoing detailed description of the inventive subject
matter, it should be appreciated that a vast number of variations
exist. It should also be appreciated that the exemplary embodiment
or exemplary embodiments are only examples, and are not intended to
limit the scope, applicability, or configuration of the inventive
subject matter in any way. Rather, the foregoing detailed
description will provide those skilled in the art with a convenient
road map for implementing an exemplary embodiment of the inventive
subject matter. It being understood that various changes may be
made in the function and arrangement of elements described in an
exemplary embodiment without departing from the scope of the
inventive subject matter as set forth in the appended claims.
* * * * *