U.S. patent application number 10/640764 was filed with the patent office on 2005-02-17 for thermal barrier coating for reduced sintering and increased impact resistance, and process of making same.
This patent application is currently assigned to General Electric Company. Invention is credited to Boutwell, Brett, Spitsberg, Irene, Venkataramani, Venkat S..
Application Number | 20050036891 10/640764 |
Document ID | / |
Family ID | 33565270 |
Filed Date | 2005-02-17 |
United States Patent
Application |
20050036891 |
Kind Code |
A1 |
Spitsberg, Irene ; et
al. |
February 17, 2005 |
Thermal barrier coating for reduced sintering and increased impact
resistance, and process of making same
Abstract
A composition is disclosed that includes an at least partially
stabilized zirconia matrix with a stabilizer and a pentavalent
oxide dopant. A coated article is disclosed for use in a high
temperature a gas turbine. The coated article can include an
yttria-stabilized zirconia, and a pentavalent oxide dopant. The
pentavalent oxide dopant can reduce sintering of the thermal
barrier coating.
Inventors: |
Spitsberg, Irene; (Loveland,
OH) ; Venkataramani, Venkat S.; (Clifton Park,
NY) ; Boutwell, Brett; (Liberty Township,
OH) |
Correspondence
Address: |
Schwegman, Lundberg, Woessner & Kluth, P.A.
P.O. Box 2938
Minneapolis
MN
55402
US
|
Assignee: |
General Electric Company
|
Family ID: |
33565270 |
Appl. No.: |
10/640764 |
Filed: |
August 14, 2003 |
Current U.S.
Class: |
416/241R ;
428/633 |
Current CPC
Class: |
C23C 28/3455 20130101;
C23C 28/345 20130101; F01D 5/288 20130101; C23C 14/083 20130101;
C23C 28/322 20130101; C23C 30/00 20130101; C23C 4/02 20130101; C23C
28/3215 20130101; C23C 28/325 20130101; Y10T 428/12618 20150115;
C23C 4/11 20160101; C23C 28/321 20130101 |
Class at
Publication: |
416/241.00R ;
428/633 |
International
Class: |
B63H 001/26 |
Goverment Interests
[0001] This invention was made, at least in part, with a grant from
the Government of the United States (Contract No. N00019-96-C-0176,
from the Department of the Navy). The Government may have certain
rights to the invention.
Claims
What is claimed is:
1. A composition comprising: a ceramic matrix including an at least
partially stabilized zirconia and at least one pentavalent oxide
dopant in a concentration from about 1 mol percent to about 4 mol
percent.
2. The composition according to claim 1, wherein the at least at
least one pentavalent oxide dopant is in a concentration from about
1.3 mol percent to about 1.89 mol percent.
3. The composition according to claim 1, wherein the at least at
least one pentavalent oxide dopant is in a concentration of about
1.6 mol percent.
4. The composition according to claim 1, wherein the at least
partially stabilized zirconia is stabilized from at least one of
yttria, calcia, magnesia, ceria, and combinations thereof.
5. The composition according to claim 1, wherein the at least
partially stabilized zirconia includes yttria in a range from about
4% to about 8%.
6. The composition according to claim 1, wherein the pentavalent
oxide is selected from tantalum oxide, niobium oxide, and
combinations thereof.
7. The composition according to claim 1, further including at least
one trivalent oxide selected from, lanthanum oxide, ytterbium
oxide, gadolinium oxide, neodymium oxide, and combinations
thereof.
8. The composition according to claim 1, wherein the pentavalent
dopant includes one selected from tantala (Ta.sub.2O.sub.5) and
tantalum oxide as a non-stoichiometric solid solution, in a major
amount and at least one other pentavalent oxide.
9. The composition according to claim 1, wherein the pentavalent
dopant includes one selected from niobia (Nb.sub.2O.sub.5) and
niobium oxide as a non-stoichiometric solid solution, in a major
amount and at least one other pentavalent oxide.
10. A coated article, comprising: a superalloy substrate; a bond
coat disposed above the superalloy substrate; a ceramic interface
disposed above the bond coat; and a thermal barrier coating
disposed above the ceramic interface including an yttria-stabilized
zirconia (YSZ) and a pentavalent oxide dopant in a concentration
from about 1 mol percent to about 4 mol percent.
11. The coated article according to claim 10, wherein the yttrium
in the YSZ is about 7%.
12. The coated article according to claim 10, wherein the
pentavalent oxide is selected from Ta.sub.2O.sub.5, tantalum oxide,
Nb.sub.2O.sub.5, niobium oxide, and a combination thereof, and
wherein the pentavalent oxide is present in a range from about 1.3
mol % to about 1.9 mol %.
13. The coated article according to claim 10, wherein the
pentavalent oxide is selected from, tantalum oxide, niobium oxide,
and combinations thereof.
14. The coated article according to claim 10, wherein the
pentavalent oxide dopant includes one selected from tantala
(Ta.sub.2O.sub.5) and tantalum oxide as a non-stoichiometric solid
solution, in a major amount and at least one other pentavalent
oxide, and wherein the pentavalent oxide dopant is in a
concentration range from about 1.2 mol percent to about 2 mol
percent.
15. The coated article according to claim 10, wherein the
pentavalent oxide dopant includes one selected from niobia
(Nb.sub.2O.sub.5) and niobium oxide as a non-stoichiometric solid
solution, in a major amount and at least one other pentavalent
oxide, and wherein the pentavalent oxide dopant is in a
concentration range from about 1.2 mol percent to about 2 mol
percent.
16. A coated turbine blade comprising: a turbine blade substrate
including a superalloy; a turbine blade coating above the turbine
blade substrate, wherein the coating is a composition including an
yttria-stabilized zirconia (YSZ) matrix and a pentavalent oxide
dopant in a concentration from about 1 mol percent to about 4 mol
percent.
17. The coated turbine blade according to claim 16, wherein the
turbine blade coating includes a bond coat including aluminum, and
wherein the pentavalent oxide dopant includes tantala in a range
from about 1.3 mol % to about 1.9 mol %.
18. The coated turbine blade according to claim 16, wherein the
turbine blade coating includes a bond coat including aluminum, and
wherein the pentavalent oxide dopant includes niobia in a range
from about 1.3 mol % to about 1.9 mol %.
19. The coated turbine blade according to claim 16, wherein the
turbine blade coating includes a bond coat including aluminum, and
wherein the pentavalent oxide dopant includes vanadia in a range
from about 1.3 mol % to about 1.9 mol %.
20. A system comprising: a gas turbine, and within the gas turbine
a turbine blade, including: a superalloy substrate; a bond coating
disposed above the superalloy substrate; a ceramic interface
disposed above the bond coating; and a thermal barrier coating
disposed above the ceramic interface including an yttria-stabilized
zirconia (YSZ) and a pentavalent oxide dopant in a concentration
from about 1 mol percent to about 4 mol percent.
21. The system according to claim 20, wherein the pentavalent oxide
dopant includes from about 1 mol percent to about 2.2 mol percent
tantala, niobia, or a combination thereof.
Description
TECHNICAL FIELD
[0002] Embodiments relate to a thermal barrier coating. More
particularly, embodiments relate to an article with a thermal
barrier coating which is used in the gas path environment of a gas
turbine engine. In particular, an embodiment relates to a gas
turbine system which includes a coated turbine blade which acts as
a thermal barrier coating.
TECHNICAL BACKGROUND
[0003] A thermal barrier coating (TBC) system may be used to
protect the components of a gas turbine engine that are subjected
to the highest material temperatures. The TBC system usually
includes a bond coat that is deposited upon a superalloy substrate,
and a ceramic TBC that is deposited upon the bond coat. The TBC
acts as a thermal insulator against the heat of the hot combustion
gas. The bond coat bonds the TBC to the substrate and also inhibits
oxidation and corrosion of the substrate.
[0004] One currently used TBC is yttria-stabilized zirconia (YSZ),
which is zirconia (zirconium oxide) with from about 3 to about 12
percent by weight yttria (yttrium oxide) added to stabilize the
zirconia against phase changes that otherwise occur as the TBC is
heated and cooled during fabrication and service. The YSZ is
deposited by a physical vapor deposition process such as electron
beam physical vapor deposition (EBPVD). In this deposition process,
the grains of the YSZ form as columnar structures that extend
generally outwardly from and perpendicular to the substrate and the
bond coat.
[0005] To be effective, the TBC system must have a low thermal
conductivity and be strongly adherent to the article to which it is
bonded under contemplated use conditions. To promote adhesion and
to extend the service life of a TBC system, an oxidation-resistant
bond coat is usually employed. Bond coats are typically in the form
of overlay coatings such as MCrAlX, where M is a transition metal
such as iron, cobalt, and/or nickel, and X is yttrium or another
rare earth element. Bond coats are also diffusion coatings such as
simple aluminide of platinum aluminide. A notable example of a
diffusion aluminide bond coat contains a platinum intermetallic,
e.g. NiPtAl. When a diffusion bond coat is applied, a zone of
interdiffusion forms beneath a diffusion bond coat. This zone is
typically referred to as a diffusion zone.
[0006] During exposure of the ceramic TBC and subsequent exposures
to high temperatures such as during ordinary service use thereof,
bond coats of the type described above oxidize to form a tightly
adherent alumina scale that protects the underlying structure from
catastrophic oxidation.
[0007] The columnar structure of the TBC system is of particular
importance to adherence of the coating and to the coating
maintaining a low thermal conductivity. Beside gaps between
columns, there also exists a fine porosity within subgrains in the
columnar structure. The fine porosity is sometimes observed to be
oriented substantially orthogonal to the columns.
[0008] As the YSZ is cycled to elevated temperatures during
service, sintering creates the problems of both the large-grain,
inter-columnar porosity and the subgrain, fine porosity being
gradually closed. As a result, the ability of the YSZ to
accommodate thermal expansion strains gradually is reduced, and the
thermal conductivity of the YSZ gradually increases by about 20
percent or more.
[0009] It has been recognized that the addition of sintering
inhibitors to the YSZ reduces the tendency of the gaps between the
columnar grains to close by sintering during service of the thermal
barrier coating. A number of sintering inhibitors have been
proposed. However, these sintering inhibitors have various
shortcomings, and there is a need for more effective sintering
inhibitors.
[0010] Some of the physical demands of a gas turbine blade include
operation in extreme environments. One condition which a gas
turbine blade is subjected to is the erosive effect of small
particles which pass across the turbine blade. The small particles
can be generated a part of the combustion process inside a gas
turbine. Another condition which a gas turbine blade is subjected
to is foreign objects which come into the gas stream.
[0011] What is needed is a TBC that avoids at least some of the
problems that existed in the prior art.
SUMMARY
[0012] A component article of a gas turbine engine is disclosed.
The component article is applicable to a turbine blade or turbine
vane. The component article includes a body that serves as a
substrate. Overlying and contacting the substrate is a thermal
barrier coating system such as a bond coat. The bond coat includes
an optional metal first layer that is a metal such as platinum or
the like. The bond coat also includes a metal upper layer that is a
metal such as aluminum or the like.
[0013] In one embodiment, the bond coat includes a diffusion zone
that is the result of interdiffusion of material from the bond coat
with material from the substrate. In one embodiment, the process
that deposits the metal upper layer above the substrate is
performed at elevated temperature, so that during deposition, the
material of the metal upper layer interdiffuses into and with the
material of the substrate to form the diffusion zone.
[0014] The structure of the turbine blade is completed with a
ceramic thermal barrier coating that overlies and contacts the bond
coat surface and the alumina scale thereon. The ceramic thermal
barrier coating includes an yttria-stabilized zirconia with at
least one pentavalent oxide dopant in a concentration from about 1
mol percent to about 4 mol percent.
[0015] The bond coat includes the optional metal first layer, if
present, the metal upper layer, and the alumina scale. In one
embodiment, the bond coat is a diffusion aluminide bond coat that
is formed by depositing an aluminum-containing metal upper layer
over the substrate, and by interdiffusing the aluminum-containing
metal upper layer with the substrate. In one embodiment, the bond
coat is a simple diffusion aluminde. In one embodiment, the bond
coat is a more complex diffusion aluminide that includes another
layer such as the metal first layer. In one embodiment, the metal
first layer is a platinum layer.
[0016] In one embodiment, the entire bond coat includes a
platinum-aluminide diffusion aluminide. In this embodiment, a
platinum-containing metal first layer is first deposited onto the
surface of the substrate. In one embodiment, other metals are used
in place of or in addition to the platinum to form the metal first
layer.
[0017] After formation of the metal first layer, if present, the
metal upper layer is deposited above the substrate, and upon the
metal first layer if present, by any operable approach. In one
embodiment, an alumina scale forms at the bond coat surface by
oxidation of the aluminum in the bond coat.
[0018] The ceramic thermal barrier coating is deposited by a
process such as physical vapor deposition process such as electron
beam physical vapor deposition (EBPVD), or by the process of plasma
spray deposition. In one embodiment, the ceramic thermal barrier
coating is a YSZ ceramic matrix with at least one pentavalent oxide
dopant added.
[0019] Examples include YSZ that has been modified with additions
of a "third" oxide. In one embodiment, the "third" oxide includes a
pentavalent oxide selected from vanadium oxide, tantalum oxide,
niobium oxide, combinations thereof, and the like.
[0020] In one embodiment, the "third" oxide includes in addition to
at least one pentavalent oxide, a trivalent oxide selected from
lanthanum oxide, combinations thereof, and the like. In one
embodiment, the "third" oxide includes one selected ytterbium
oxide, gadolinium oxide, neodymium oxide, combinations thereof, and
the like. In each enumerated embodiment, the "third" oxide is
co-deposited with the YSZ.
[0021] When prepared by a PVD process, the thermal barrier coating
is formed generally of a plurality of columnar grains of the
ceramic material that are affixed at their roots to the bond coat
and the alumina scale. In some locations of the thermal barrier
coating, there are gaps that add to the insulative quality of the
thermal barrier coating.
[0022] Processing is carried out by forming the optional bond coat
over the substrate. Additionally, the optional platinum layer can
be formed before forming the bond coat. To form the alumina scale,
the bond coat can be thermally treated. The thermal barrier coating
is formed by a deposition process selected from electron beam
physical vapor deposition (EBPVD) and plasma spraying.
[0023] These and other embodiments are set forth in the Detailed
Description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] In order to understand the manner in which embodiments are
obtained, a more particular description of various embodiments
briefly described above will be rendered by reference to the
appended drawings. Understanding that these drawings depict only
typical embodiments that are not necessarily drawn to scale and are
not therefore to be considered to be limiting of its scope, the
embodiments will be described and explained with additional
specificity and detail through the use of the accompanying drawings
in which:
[0025] FIG. 1 depicts a component article of a gas turbine engine
such as a turbine blade or turbine vane;
[0026] FIG. 2 is a computer image cross section, through a portion
of the turbine blade depicted in FIG. 1; and
[0027] FIG. 3 is a process flow diagram according to an
embodiment.
DETAILED DESCRIPTION
[0028] The following description includes terms, such as first,
second, etc. that are used for descriptive purposes only and are
not to be construed as limiting. In the following detailed
description, reference is made to the accompanying drawings, which
form a part hereof. These drawings show, by way of illustration,
specific embodiments in which the invention may be practiced. In
the drawings, some of the like numerals describe substantially
similar components throughout the several views. These embodiments
are described in sufficient detail to enable those skilled in the
art to practice the invention. Other embodiments may be used and
structural changes may be made without departing from the scope of
the several embodiments. Additionally, where compositions are
given, if a composition is given with a percentage that is not
modified by a term such as mol %, volume %, etc. it is understood
that the percentage is given in weight percent.
[0029] FIG. 1 depicts a component article of a gas turbine engine
such as a turbine blade or turbine vane, and in this illustration a
turbine blade 100. The turbine blade 100 is formed of any operable
material. The turbine blade 100 includes an airfoil section 110
against which the flow of exhaust gas is directed. The turbine vane
or nozzle has a similar appearance in respect to the pertinent
airfoil section, but typically includes other end structure to
support the airfoil. The turbine blade 100 is mounted to a turbine
disk (not shown) by a dovetail 112 that extends downwardly from the
airfoil 110 and engages a slot on the turbine disk. A platform 114
extends longitudinally outwardly from the area where the airfoil
110 is joined to the dovetail 112.
[0030] FIG. 2 is a computer image cross section, through a portion
of the turbine blade 100. The turbine blade 100 is depicted in FIG.
2 as the airfoil section 110 of FIG. 1, and it is enumerated in
FIG. 2 as item 200. The turbine blade 200 has a body that serves as
a substrate 216 with a substrate surface 218. Overlying and
contacting the substrate surface 218, and also extending downwardly
into the substrate 216, is a thermal barrier coating system 220
including a protective coating 222, which in this case is termed a
bond coat 222. The bond coat 222 is thin and generally planar while
conforming to and being bonded to the surface 218 of the substrate
216. In one embodiment, the bond coat 222 is in a thickness range
from about 0.0005 inch to about 0.0 10 inch.
[0031] In one embodiment, the bond coat 222 includes an optional
metal first layer 224 that is a metal such as platinum or the like.
The bond coat 222 also includes a metal upper layer 226 that is a
metal such as aluminum or the like. In one embodiment, the bond
coat 222 includes a diffusion zone 228 that is the result of
interdiffusion of material from the bond coat 222 with material
from the substrate 216. In one embodiment, the process which
deposits the metal upper layer 226 above the substrate surface 218
is performed at elevated temperature, so that during deposition,
the material of the metal upper layer 226 interdiffuses into and
with the material of the substrate 216, to form the diffusion zone
228. The diffusion zone 228, indicated by the dashed lines in FIG.
2, is a part of the thermal barrier coating system but it extends
downward into the substrate 216.
[0032] In one embodiment, the bond coat 222 has an outwardly facing
bond coat surface 230 remote from the surface 218 of the substrate
216. In one embodiment, a ceramic interface such as alumina
(aluminum oxide, or Al.sub.20.sub.3) scale 232 that forms at this
bond coat surface 230 by oxidation of the aluminum in the bond coat
220.
[0033] The structure of the turbine blade 200 is completed with a
ceramic thermal barrier coating 234 that overlies and contacts the
bond coat surface 230 and the alumina scale 232 thereon. The
ceramic thermal barrier coating 234 includes an yttria-stabilized
zirconia with at least one pentavalent oxide dopant in a
concentration from about 1 mol percent to about 4 mol percent. In
one embodiment, the pentavalent oxide dopant is in a concentration
from about 1.3 mol percent to about 1.9 mol percent. In one
embodiment, the pentavalent oxide dopant is in a concentration from
about 1.4 mol percent to about 1.8 mol percent. In one embodiment,
the pentavalent oxide dopant is in a concentration of about 1.6 mol
percent.
[0034] Substrate Materials
[0035] Reference is again made to FIG. 1. In one embodiment, the
component article includes a component of a gas turbine engine such
as a gas turbine blade 100 or vane (or "nozzle", as the vane is
sometimes called). In one embodiment, the component article
includes a single crystal substrate. In one embodiment, the
component article is a preferentially oriented polycrystal, or a
randomly oriented polycrystal. In one embodiment, the component
article is made of a nickel-base superalloy for the substrate 216
(FIG. 2). As used herein, "nickel-base" means that the composition
has more nickel present than any other element.
[0036] The nickel-base superalloys are typically of a composition
that is strengthened by the precipitation of gamma-prime phase or a
related phase. In one embodiment, the nickel-base alloy has a
composition, in weight percent, of from about 4 to about 20 percent
cobalt, from about 1 to about 10 percent chromium, from about 5 to
about 7 percent aluminum, from 0 to about 2 percent molybdenum,
from about 3 to about 8 percent tungsten, from about 4 to about 12
percent tantalum, from 0 to about 2 percent titanium, from 0 to
about 8 percent rhenium, from 0 to about 6 percent ruthenium, from
0 to about 1 percent niobium, from 0 to about 0.1 percent carbon,
from 0 to about 0.01 percent boron, from 0 to about 0.1 percent
yttrium, from 0 to about 1.5 percent hafnium, balance nickel and
incidental impurities.
[0037] In one embodiment, an alloy composition for the substrate
216 is Rene' N5, which has a nominal composition in weight percent
of about 7.5 percent cobalt, about 7 percent chromium, about 6.2
percent aluminum, about 6.5 percent tantalum, about 5 percent
tungsten, about 1.5 percent molybdenum, about 3 percent rhenium,
about 0.05 percent carbon, about 0.004 percent boron, about 0.15
percent hafnium, up to about 0.01 percent yttrium, balance nickel
and incidental impurities.
[0038] In one embodiment, an alloy composition for the substrate
216 is Rene' N6, which has a nominal composition in weight percent
of about 12.5 percent cobalt, about 4.2 percent chromium, about 1.4
percent molybdenum, about 5.75 percent tungsten, about 5.4 percent
rhenium, about 7.2 percent tantalum, about 5.75 percent aluminum,
about 0.15 percent hafnium, about 0.05 percent carbon, about 0.004
percent boron, about 0.01 percent yttrium, balance nickel and
incidental impurities.
[0039] In one embodiment, an alloy composition for the substrate
216 is Rene' 142, which has a nominal composition, in weight
percent, of about 12 percent cobalt, about 6.8 percent chromium,
about 1.5 percent molybdenum, about 4.9 percent tungsten, about 6.4
percent tantalum, about 6.2 percent aluminum, about 2.8 percent
rhenium, about 1.5 percent hafnium, about 0.1 percent carbon, about
0.015 percent boron, balance nickel and incidental impurities.
[0040] In one embodiment, an alloy composition for the substrate
216 is CMSX-4, which has a nominal composition in weight percent of
about 9.60 percent cobalt, about 6.6 percent chromium, about 0.60
percent molybdenum, about 6.4 percent tungsten, about 3.0 percent
rhenium, about 6.5 percent tantalum, about 5.6 percent aluminum,
about 1.0 percent titanium, about 0.10 percent hafnium, balance
nickel and incidental impurities.
[0041] In one embodiment, an alloy composition for the substrate
216 is CMSX-10, which has a nominal composition in weight percent
of about 7.00 percent cobalt, about 2.65 percent chromium, about
0.60 percent molybdenum, about 6.40 percent tungsten, about 5.50
percent rhenium, about 7.5 percent tantalum, about 5.80 percent
aluminum, about 0.80 percent titanium, about 0.06 percent hafnium,
about 0.4 percent niobium, balance nickel and incidental
impurities.
[0042] In one embodiment, an alloy composition for the substrate
216 is PWA 1480, which has a nominal composition in weight percent
of about 5.00 percent cobalt, about 10.0 percent chromium, about
4.00 percent tungsten, about 12.0 percent tantalum, about 5.00
percent aluminum, about 1.5 percent titanium, balance nickel and
incidental impurities.
[0043] In one embodiment, an alloy composition for the substrate
216 is PWA1484, which has a nominal composition in weight percent
of about 10.00 percent cobalt, about 5.00 percent chromium, about
2.00 percent molybdenum, about 6.00 percent tungsten, about 3.00
percent rhenium, about 8.70 percent tantalum, about 5.60 percent
aluminum, about 0.10 percent hafnium, balance nickel and incidental
impurities.
[0044] In one embodiment, an alloy composition for the substrate
216 is Mx-4, which has a nominal composition as set forth in U.S.
Pat. No. 5,482,789, in weight percent, of from about 0.4 to about
6.5 percent ruthenium, from about 4.5 to about 5.75 percent
rhenium, from about 5.8 to about 10.7 percent tantalum, from about
4.25 to about 17.0 percent cobalt, from 0 to about 0.05 percent
hafnium, from 0 to about 0.06 percent carbon, from 0 to about 0.01
percent boron, from 0 to about 0.02 percent yttrium, from about 0.9
to about 2.0 percent molybdenum, from about 1.25 to about 6.0
percent chromium, from 0 to about 1.0 percent niobium, from about
5.0 to about 6.6 percent aluminum, from 0 to about 1.0 percent
titanium, from about 3.0 to about 7.5 percent tungsten, and wherein
the sum of molybdenum plus chromium plus niobium is from about 2.15
to about 9.0 percent, and wherein the sum of aluminum plus titanium
plus tungsten is from about 8.0 to about 15.1 percent, balance
nickel and incidental impurities.
[0045] The use of the foregoing embodiments is not limited to these
enumerated alloys, and has broader applicability.
[0046] Bond Coat Materials
[0047] The bond coat 222 includes the optional metal first layer
224, if present, the metal upper layer 226, and the alumina scale
232.
[0048] In one embodiment, the bond coat 222 is a diffusion
aluminide bond coat which is formed by depositing an
aluminum-containing metal upper layer 226 over the substrate 216,
and by interdiffusing the aluminum-containing metal upper layer 226
with the substrate 216. In one embodiment, the bond coat 222 is a
simple diffusion aluminde. In one embodiment, the bond coat 222 is
a more complex diffusion aluminide that includes another layer such
as the metal first layer 224. In one embodiment, the metal first
layer 224 is a platinum layer.
[0049] Whether the bond coat 222 is a simple diffusion aluminide or
a more complex diffusion aluminide, the aluminum-containing metal
upper layer 226 may be doped with other elements that modify the
bond coat 222. In one embodiment, the bond coat 222 includes an
overlay coating known as an MCrAlX coating. The terminology
"MCrAlX" is a shorthand term of art for a variety of families of
overlay bond coats that may be employed as environmental coatings
or bond coats in thermal barrier coating systems. In this and other
forms, M refers to nickel, cobalt, iron, and combinations thereof.
In some of these protective coatings, the chromium may be omitted.
The X denotes elements such as hafnium, zirconium, yttrium,
tantalum, rhenium, ruthenium, palladium, platinum, silicon,
titanium, boron, carbon, and combinations thereof. Specific
compositions are known in the art. Some examples of MCrAlX
compositions include, for example, NiAlCrZr and NiAlZr, but this
listing of examples is not to be taken as limiting.
[0050] In one embodiment, the entire bond coat 222 includes a
platinum-aluminide diffusion aluminide. In this embodiment, a
platinum-containing metal first layer 224 is first deposited onto
the surface 218 of the substrate 216. In one embodiment, the
platinum-containing metal first layer 224 is deposited by
electrodeposition. In one embodiment, electrodeposition is
accomplished by placing a platinum-containing solution into a
deposition tank and depositing platinum from the solution onto the
surface 218 of the substrate 216. An operable platinum-containing
aqueous solution is Pt(NH.sub.3).sub.4HPO.sub.4 having a
concentration of about 4-20 grams per liter of platinum, and the
voltage/current source is operated at about 1/2-10 amperes per
square foot of facing article surface. In one embodiment, the
platinum metal first layer 224, is deposited in 1-4 hours at a
temperature of 190-200.degree. F. In one embodiment, the platinum
metal first layer 224 is formed in a thickness range from about
0.00004 inch to about 0.00024 inch. In one embodiment, the platinum
metal first layer 224 is about 0.0002 inch thick.
[0051] In one embodiment, other metals are used in place of or in
addition to the platinum to form the metal first layer 224. Such
metals and their combinations are known in the art.
[0052] After formation of the metal first layer 224, if present,
the metal upper layer 226 is deposited above the substrate 216, and
upon the metal first layer 224 if present, by any operable
approach. In one embodiment, chemical vapor deposition (CVD) is
used to form the metal upper layer 226. In that approach, a
hydrogen halide activator gas, such as hydrogen chloride, is
contacted with aluminum metal or an aluminum alloy to form the
corresponding aluminum halide gas. Halides of any modifying
elements are formed by the same technique. The aluminum halide (or
mixture of aluminum halide and halide of the modifying element, if
any) contacts the platinum-containing metal first layer 224 that
overlies the substrate 216, depositing the aluminum thereon. In one
embodiment, the deposition occurs at elevated temperature such as
from about 1,825.degree. F. to about 1,975.degree. F. so that the
deposited aluminum atoms interdiffuse into the substrate 216 during
a 4 to 20 hour cycle.
[0053] In one embodiment, an alumina (aluminum oxide, or
Al.sub.20.sub.3) scale 232 forms at this bond coat surface 230 by
oxidation of the aluminum in the bond coat 220 at the bond coat
surface 230. Where the metal upper layer is a complex aluminum
compound, a modified "alumina" scale 232 correspondingly forms the
scale 232.
[0054] Thermal Barrier Coatings
[0055] The ceramic thermal barrier coating 234 is deposited by a
process such as physical vapor deposition process such as electron
beam physical vapor deposition (EBPVD), or by the process of plasma
spray deposition. In one embodiment, the ceramic thermal barrier
coating 234 has a thickness from about 0.003 inch to about 0.010
inch thick. In one embodiment, the ceramic thermal barrier coating
234 has a thickness of about 0.005 inch thick.
[0056] In one embodiment, the ceramic thermal barrier coating 234
is a YSZ, which is zirconium oxide containing from about 3 to about
12 weight percent. In one embodiment, the ceramic thermal barrier
coating 234 is from about 4 to about 8 weight percent, of yttrium
oxide. Additionally, at least one pentavalent oxide dopant is
added.
[0057] Examples include YSZ that has been modified with additions
of a "third" oxide. In one embodiment, the "third" oxide includes a
pentavalent oxide selected from tantalum oxide, niobium oxide,
combinations thereof, and the like.
[0058] In one embodiment, the "third" oxide includes in addition to
at least one pentavalent oxide, a trivalent oxide such as lanthanum
oxide, and the like. In one embodiment, the "third" oxide includes
one selected ytterbium oxide, gadolinium oxide, neodymium oxide,
combinations thereof, and the like. In each enumerated embodiment,
the "third" oxide is co-deposited with the pentavalent oxide and
the YSZ.
[0059] In one embodiment, the ceramic thermal barrier coating 234
includes a ceramic matrix of a doped zirconia with the addition of
at least one pentavalent oxide. In one embodiment, the zirconia
ceramic matrix is at least partially stabilized with calcia and the
addition of at least one pentavalent oxide. In one embodiment, the
zirconia ceramic matrix is at least partially stabilized with
magnesia and the addition of at least one pentavalent oxide. In one
embodiment, the zirconia ceramic matrix is at least partially
stabilized with ceria and the addition of at least one pentavalent
oxide. In one embodiment, the zirconia ceramic matrix is at least
partially stabilized with a combination of at least two of the
above stabilizers and the addition of at least one pentavalent
oxide.
[0060] In one embodiment, the zirconia ceramic matrix includes YSZ
with about 4 to about 8% by weight of yttria (which can be referred
to as 4-8 YSZ). In this embodiment, the 4-8 YSZ matrix includes a
pentavalent oxide dopant in a concentration from about 1 mol
percent to about 4 mol percent. In one embodiment, the 4-8 YSZ
matrix includes a pentavalent oxide dopant in a concentration of
about 1.6 mol percent.
[0061] In one embodiment, the pentavalent oxide includes tantala,
Ta.sub.2O.sub.5. In one embodiment, the pentavalent oxide includes
tantala in a major amount and at least one other pentavalent oxide
such as niobia or niobium oxide. In an alternative embodiment, the
pentavalent oxide includes a tantalum oxide as a non-stoichiometric
solid solution within the ceramic matrix. In another alternative
embodiment, the pentavalent oxide includes a tantalum oxide in a
major amount as a non-stoichiometric solid solution within the
ceramic matrix, and at least one other pentavalent oxide such as
niobia or niobium oxide. In one embodiment, the pentavalent oxide
includes tantala in a range from about 1 mol % to about 4 mol %. In
one embodiment, the pentavalent oxide includes tantala in a range
from about 1.3 mol % to about 1.9 mol %. In one embodiment, the
pentavalent oxide includes tantala in a range from about 1.4 mol %
to about 1.8 mol %. In one embodiment, the pentavalent oxide
includes about 1.6 mol % tantala in a 7 YSZ ceramic matrix.
[0062] In one embodiment, the pentavalent oxide includes niobia,
Nb.sub.2O.sub.5. In one embodiment, the pentavalent oxide includes
niobia in a major amount and at least one other pentavalent oxide
such as tantala or tantalum oxide. In an alternative embodiment,
the pentavalent oxide includes a niobium oxide as a
non-stoichiometric solid solution within the ceramic matrix. In
another alternative embodiment, the pentavalent oxide includes a
niobium oxide in a major amount as a non-stoichiometric solid
solution within the ceramic matrix, and at least one other
pentavalent oxide such as tantala or tantalum oxide.
[0063] In one embodiment, the pentavalent oxide includes niobia in
a range from about 1 mol % to about 4 mol %. In one embodiment, the
pentavalent oxide includes niobia in a range from about 1.2 mol %
to about 1.8 mol %. In one embodiment, the pentavalent oxide
includes about 1.6 mol % niobia in a 7 YSZ ceramic matrix.
[0064] The thermal barrier coating 234 can include one of the
various ceramic matrix embodiments that are set forth herein. In
one embodiment, yttria in the thermal barrier coating 234 is
present in an amount of about 7%. The pentavalent oxide is selected
from Ta.sub.2O.sub.5, tantalum oxide, Nb.sub.2O.sub.5, niobium
oxide, and a combination thereof, and is present in a range from
about 1 mol % to about 4 mol %. In one embodiment, the pentavalent
oxide is selected from Ta.sub.2O.sub.5, tantalum oxide,
Nb.sub.2O.sub.5, niobium oxide, and a combination thereof, and is
present in a range from about 1.3 mol % to about 3 mol %. In one
embodiment, the pentavalent oxide is selected from Ta.sub.2O.sub.5,
tantalum oxide, Nb.sub.2O.sub.5, niobium oxide, and a combination
thereof, Ta.sub.2O.sub.5, tantalum oxide, Nb.sub.2O.sub.5, niobium
oxide, and a combination thereof, and is present in a range from
about 1.5 mol % to about 2 mol %. In one embodiment, the
pentavalent oxide is selected from Ta.sub.2O.sub.5, tantalum oxide,
Nb.sub.2O.sub.5, niobium oxide, and a combination thereof, and is
present at about 1.6 mol %.
[0065] As illustrated schematically in FIG. 2, when prepared by a
PVD process, the thermal barrier coating 234 is formed generally of
a plurality of columnar grains 236 of the ceramic material that are
affixed at their roots to the bond coat 222 and the alumina scale
232. The columnar grains 236 have grain surfaces 238. In some
locations of the thermal barrier coating 234, there are gaps 240,
whose size is exaggerated in FIG. 2 for the purposes of
illustration, between the grains 236 and their facing grain
surfaces 238.
[0066] In one embodiment, the ceramic thermal barrier coating 234
is formed by EBPVD that forms a subgrain 242. The subgrain 242 is
illustrated schematically in a selected portion of some of the
columnar grains 236. In FIG. 2, the subgrain 242 includes a
subgrain boundary and a subgrain body. The subgrain boundary is
depicted schematically as a diagonal line. The subgrain body is
depicted schematically as the space between two diagonal lines.
[0067] This morphology of the thermal barrier coating 236 including
the columnar grains 236 with their corresponding gaps 240 and the
subgrains 242 is beneficial to the functioning of the thermal
barrier coating 236. The gaps 240 allow the substrate 216, the bond
coat 222 including the alumina scale 232, and the thermal barrier
coating 234 to expand and contract without significantly damaging
morphological changes therein. Because the thermal barrier coating
234 is a ceramic material, it has a generally low ductility so that
the accumulated stresses would be likely to cause failure. With the
gaps 240 present, however, the in-plane stresses in the thermal
barrier coating 236 are developed across only one or at most a
group of a few of the columnar grains 236. That is, all of the
columnar grains 236 have in-plane stresses, but the magnitude of
the in-plane stresses are relatively low because the strains do not
accumulate over long distances. The result is that the thermal
barrier coating 234 with the columnar grains 236 and gaps 240 is
less likely to fail by in-plane overstressing during service.
Additionally, the gaps 240 are filled with air, which when
relatively stagnant between the grains 236 is an effective thermal
insulator, aiding the thermal barrier coating 234 in performing its
primary role.
[0068] FIG. 3 is a block diagram of a process embodiment. The
process 300 includes forming the thermal barrier coating, and
optionally forming the bond coating.
[0069] At 310, an optional bond coat is formed over the
substrate.
[0070] At 312, the optional platinum layer is formed before forming
the bond coat.
[0071] At 314, the bond coat is optionally thermally treated to
form the "alumina" scale 232 as set forth herein according to
several embodiments.
[0072] At 320, the thermal barrier coating is formed by a
deposition process selected from EBPVD and plasma spraying.
EXAMPLE 1
[0073] An EB-PVD technique was used to form a coating on a
substrate. The coating was 7 YSZ that included about 1.6 mol % of
Ta.sub.2O.sub.5. After the TBC was applied, thermal cycling (TC)
was done to obtain a metric on sintering resistance. The coating
was heated to about 1,200.degree. C. for about 2 hours in air.
After the thermal cycling, the coated substrate had an observed
change in thermal conductivity from about 1.58 W/m K before TC to
about 1.64 W/m K after TC, respectively. Evaluation of the thermal
conductivity was conducted by the laser flash method known in the
art.
EXAMPLE 2
[0074] An EB-PVD technique is used to form a coating on a
substrate. The coating is a 4-8 YSZ that includes a pentavalent
oxide dopant in a concentration from about 1 mol percent to about 4
mol percent. After forming the coating on the substrate, the
coating on the substrate is exposed to about 1,200.degree. C. for
about 2 hours in air to obtain a metric on sintering resistance.
After the heat treating of the coating, thermal conductivity of the
coating has increased from about 2% to about 10%. In one
embodiment, thermal conductivity of the coating has increased more
than 10%, but less than about 20%.
EXAMPLE 3
[0075] An EB-PVD technique is used to form a coating on a
substrate. The coating is a 7 YSZ that includes a pentavalent oxide
dopant in a concentration from about 1.2 mol percent to about 2.2
mol percent. After forming the coating on the substrate, the
coating on the substrate is exposed to about 1,200.degree. C. for
about 2 hours in air to obtain a metric on sintering resistance.
After the heat treating of the coating, thermal conductivity of the
coating has increased from about 2% to about 9%.
COMPARATIVE EXAMPLE
[0076] An EB-PVD technique was used to form a coating on a
substrate. The coating was a 7 YSZ. After the TBC was applied, TC
was done by heating the coating to about 1,200.degree. C. for about
2 hours in air. Seven baseline samples were so processed, and an
average of their tests was taken for the baseline numbers. After
the TC the coated substrate had an observed change in thermal
conductivity from about 1.53 W/m K to about 2.02 W/m K.
[0077] Gas Turbines
[0078] In one embodiment, a system is disclosed that includes a gas
turbine. In one embodiment, the gas turbine includes a composition
and structure similar to the computer drawing depicted in FIG. 2.
In one embodiment, the gas turbine includes a coated article
according to embodiments set forth in this disclosure such as is
depicted in FIG. 2. In one embodiment, the gas turbine includes a
turbine blade according to embodiments set forth in this disclosure
such as is depicted in FIG. 1.
[0079] It is emphasized that the Abstract is provided to comply
with 37 C.F.R. .sctn. 1.72(b) requiring an Abstract that will allow
the reader to quickly ascertain the nature and gist of the
technical disclosure. It is submitted with the understanding that
it will not be used to interpret or limit the scope or meaning of
the claims.
[0080] In the foregoing Detailed Description, various features are
grouped together in a single embodiment for the purpose of
streamlining the disclosure. This method of disclosure is not to be
interpreted as reflecting an intention that the claimed embodiments
of the invention require more features than are expressly recited
in each claim. Rather, as the following claims reflect, inventive
subject matter lies in less than all features of a single disclosed
embodiment. Thus the following claims are hereby incorporated into
the Detailed Description of Embodiments of the Invention, with each
claim standing on its own as a separate preferred embodiment.
[0081] It will be readily understood to those skilled in the art
that various other changes in the details, material, and
arrangements of the parts and method stages which have been
described and illustrated in order to explain the nature of this
invention may be made without departing from the principles and
scope of the invention as expressed in the subjoined claims.
* * * * *