U.S. patent application number 16/034801 was filed with the patent office on 2019-01-17 for thermal barrier coatings for components in high-temperature mechanical systems.
The applicant listed for this patent is Rolls-Royce Corporation, Rolls-Royce North American Technologies, Inc.. Invention is credited to Michael Cybulsky, Matthew R. Gold, Stephanie Gong, Li Li.
Application Number | 20190017177 16/034801 |
Document ID | / |
Family ID | 64998709 |
Filed Date | 2019-01-17 |
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United States Patent
Application |
20190017177 |
Kind Code |
A1 |
Gold; Matthew R. ; et
al. |
January 17, 2019 |
THERMAL BARRIER COATINGS FOR COMPONENTS IN HIGH-TEMPERATURE
MECHANICAL SYSTEMS
Abstract
An article that includes a substrate; a first layer including
yttria and zirconia or hafnia, where the first layer has a columnar
microstructure and includes predominately the zirconia or hafnia; a
second layer on the first layer, the second layer including
zirconia or hafnia, ytterbia, samaria, and at least one of lutetia,
scandia, ceria, neodymia, europia, and gadolinia, where the second
layer includes predominately zirconia or hafnia, and where the
second layer has a columnar microstructure; and a third layer on
the second layer, the third layer including zirconia or hafnia,
ytterbia, samaria, and a rare earth oxide including at least one of
lutetia, scandia, ceria, neodymia, europia, and gadolinia, where
the third layer has a dense microstructure and has a lower porosity
than the second layer.
Inventors: |
Gold; Matthew R.; (Carmel,
IN) ; Cybulsky; Michael; (Indianapolis, IN) ;
Gong; Stephanie; (Indianapolis, IN) ; Li; Li;
(Carmel, IN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Rolls-Royce Corporation
Rolls-Royce North American Technologies, Inc. |
Indianapolis
Indianapolis |
IN
IN |
US
US |
|
|
Family ID: |
64998709 |
Appl. No.: |
16/034801 |
Filed: |
July 13, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62533422 |
Jul 17, 2017 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C04B 41/87 20130101;
F05D 2300/2118 20130101; C04B 41/009 20130101; C04B 2235/5436
20130101; C23C 28/345 20130101; C23C 28/042 20130101; B32B 18/00
20130101; C04B 2237/704 20130101; C04B 2237/343 20130101; C23C
24/08 20130101; C04B 2111/00577 20130101; F01D 5/288 20130101; C23C
28/3215 20130101; F05D 2230/312 20130101; C23C 28/3455 20130101;
C04B 2237/586 20130101; C23C 4/073 20160101; F05D 2230/90 20130101;
C04B 2235/3224 20130101; C04B 2235/76 20130101; C04B 2111/0025
20130101; F05D 2300/15 20130101; C04B 2235/5445 20130101; C04B
2237/348 20130101; C04B 41/5042 20130101; C04B 2237/588 20130101;
C23C 4/11 20160101; C23C 4/134 20160101; F05D 2300/2112 20130101;
C04B 41/009 20130101; C04B 35/565 20130101; C04B 35/806 20130101;
C04B 41/5042 20130101; C04B 41/4527 20130101; C04B 41/5045
20130101; C04B 41/526 20130101 |
International
Class: |
C23C 28/04 20060101
C23C028/04; C23C 4/11 20060101 C23C004/11; C23C 4/134 20060101
C23C004/134; F01D 5/28 20060101 F01D005/28 |
Claims
1. An article comprising: a substrate; a first layer comprising a
first base oxide comprising zirconia or hafnia and a first rare
earth oxide comprising yttria, wherein the first layer has a
columnar microstructure, wherein the first layer comprises
predominately the first base oxide; a second layer on the first
layer, the second layer comprising a second base oxide comprising
zirconia or hafnia, a second rare earth oxide comprising ytterbia,
a third rare earth oxide comprising samaria, and a fourth rare
earth oxide comprising at least one of lutetia, scandia, ceria,
neodymia, europia, and gadolinia, wherein the second layer
comprises predominately the second base oxide, and wherein the
second layer has a columnar microstructure; and a third layer on
the second layer, the third layer comprising a third base oxide
comprising zirconia or hafnia, the second rare earth oxide, the
third rare earth oxide, and a fifth rare earth oxide comprising at
least one of lutetia, scandia, ceria, neodymia, europia, and
gadolinia, wherein the third layer has a dense microstructure and
has a lower porosity than the second layer.
2. The article of claim 1, further comprising a bond coat between
the substrate and the first layer.
3. The article of claim 1, wherein the second layer comprises a
cubic phase constitution, and wherein the third layer comprises a
tetragonal prime phase constitution.
4. The article of claim 3, wherein the second layer comprises
between about 3 mol. % and about 10 mol. % ytterbia, between about
1 mol. % and about 5 mol. % gadolinia, between about 1 mol. % and
about 5 mol. % samaria, and a balance zirconia, and wherein the
third layer comprises between about 1 mol. % and about 5 mol. %
ytterbia, between about 0.1 mol. % and about 3 mol. % gadolinia,
and between about 0.1 mol. % and about 3 mol. % samaria, and a
balance zirconia.
5. The article of claim 1, wherein the third layer further
comprises alumina in a separate phase.
6. The article of claim 1, further comprising a fourth layer
comprising a fourth base oxide comprising zirconia or hafnia,
alumina, the second rare earth oxide, the third rare earth oxide,
and a sixth rare earth oxide comprising at least one of lutetia,
scandia, ceria, neodymia, europia, and gadolinia, wherein the
fourth layer has a dense microstructure and has a lower porosity
than the second layer.
7. The article of claim 6, wherein the fourth layer comprises a
tetragonal prime phase comprising the zirconia, ytterbia,
gadolinia, samaria; and an alumina phase.
8. The article of claim 7, wherein at least one of the first layer,
the second layer, the third layer, or the fourth layer is deposited
using a suspension plasma spray technique.
9. A method comprising: depositing a first plurality of particles
on a substrate to form a first layer, wherein the first plurality
of particles comprises a first base oxide comprising zirconia or
hafnia and a first rare earth oxide comprising yttria, and wherein
the first layer comprises a columnar microstructure; depositing a
second plurality of particles on the first layer using a suspension
plasma spray technique to form a second layer, wherein the second
plurality of particles comprises a second base oxide comprising
zirconia or hafnia, a second rare earth oxide comprising ytterbia,
a third rare earth oxide comprising samaria, and a fourth rare
earth oxide comprising at least one of lutetia, scandia, ceria,
neodymia, europia, and gadolinia, wherein the second layer
comprises a columnar microstructure; and depositing a third
plurality of particles using a suspension plasma spray technique to
form a third layer on the second layer, wherein the third plurality
of particles comprises a third base oxide comprising zirconia or
hafnia, the second rare earth oxide, the third rare earth oxide,
and a fifth rare earth oxide comprising at least one of lutetia,
scandia, ceria, neodymia, europia, and gadolinia, wherein the third
layer has a dense microstructure and has a lower porosity than the
second layer.
10. The method of claim 9, further comprising depositing a bond
coat on the substrate, wherein the bond coat comprises at least one
of Pt or MCrAlY, wherein M is Ni, Co, or NiCo, and wherein
depositing the first plurality of particles comprises depositing
the first plurality of particles on the bond coat.
11. The method of claim 9, wherein the third plurality of particles
further comprises alumina.
12. The method of claim 9, further comprising depositing a fourth
plurality of particles on the third layer to form a fourth layer,
wherein the fourth plurality of particles comprises a fourth base
oxide comprising zirconia or hafnia, alumina, the second rare earth
oxide comprising ytterbia, the third rare earth oxide, and a sixth
rare earth oxide comprising at least one of lutetia, scandia,
ceria, neodymia, europia, and gadolinia, wherein the fourth layer
comprises at least one of a dense microstructure or a columnar
microstructure.
13. The method of claim 9, wherein at least one of the first,
second, or third plurality of particles defines an average diameter
of about 1 .mu.m or less.
14. The method of claim 9, wherein the second plurality of
particles comprises pre-alloyed particles, wherein the pre-alloyed
particles comprise a cubic phase constitution.
15. The method of claim 9, wherein the second plurality of
particles comprises first particles comprising zirconia, second
particles comprising ytterbia, third particles comprising samaria,
and fourth particles comprising gadolinia.
16. The method of claim 15, wherein once deposited, the second
layer comprises a cubic phase constitution.
17. The method of claim 9, wherein the third plurality of particles
comprises pre-alloyed particles, wherein the pre-alloyed particles
comprise a tetragonal prime phase constitution.
18. The method of claim 9, wherein the third plurality of particles
comprises first particles comprising zirconia, second particles
comprising ytterbia, third particles comprising samaria, and fourth
particles comprising gadolinia.
19. The method of claim 18, wherein once deposited, the third layer
comprises a tetragonal prime phase constitution.
20. The method of claim 9, wherein depositing the second plurality
of particles or depositing the third plurality of particles
comprises: forming a suspension including a respective set of
particles and a solvent; introducing the suspension into a heating
plume of a plasma spray device; directing the respective set of
particles in the suspension toward the substrate with the heating
plume; and depositing the respective set of particles to form a
layer.
Description
[0001] This application claims the benefit of U.S. Provisional
Application No. 62/533,422 filed Jul. 17, 2017, which is
incorporated herein by reference in its entirety.
TECHNICAL FIELD
[0002] The present disclosure relates to thermal barrier
coatings.
BACKGROUND
[0003] Components of high-temperature mechanical systems, such as,
for example, gas turbine engines, operate in severe environments.
For example, the high-pressure turbine blades and vanes exposed to
hot gases in commercial aeronautical engines typically experience
exterior surface temperatures of about 1000.degree. C., with
short-term peaks as high as 1100.degree. C. Example components of
high-temperature mechanical systems may include a Ni-based or
Co-based super alloy substrate or a ceramic or ceramic matrix
composite substrate.
[0004] Economic and environmental concerns such as the desire for
improved efficiency and reduced emissions, continue to drive the
development of advanced gas turbine engines with higher inlet
temperatures. Substrates of high-temperature mechanical systems may
be coated with a thermal barrier coating (TBC) to reduce the
substrate temperatures in order to meet the operational limits of
the component.
SUMMARY
[0005] In some examples, the disclosure describes an article that
includes a substrate; a first layer including a first base oxide
including zirconia or hafnia and a first rare earth oxide including
yttria, where the first layer has a columnar microstructure, where
the first layer includes predominately the first base oxide; a
second layer on the first layer, the second layer including a
second base oxide including zirconia or hafnia, a second rare earth
oxide including ytterbia, a third rare earth oxide including
samaria, and a fourth rare earth oxide including at least one of
lutetia, scandia, ceria, neodymia, europia, and gadolinia, where
the second layer includes predominately the second base oxide, and
where the second layer has a columnar microstructure; and a third
layer on the second layer, the third layer including a third base
oxide including zirconia or hafnia, the second rare earth oxide,
the third rare earth oxide, and a fifth rare earth oxide including
at least one of lutetia, scandia, ceria, neodymia, europia, and
gadolinia, where the third layer has a dense microstructure and has
a lower porosity than the second layer.
[0006] In some examples, the disclosure describes a method
including depositing a first plurality of particles on a substrate
to form a first layer, where the first plurality of particles
includes a first base oxide including zirconia or hafnia and a
first rare earth oxide including yttria, and where the first layer
includes a columnar microstructure; depositing a second plurality
of particles on the first layer using a suspension plasma spray
technique to form a second layer, where the second plurality of
particles includes a second base oxide including zirconia or
hafnia, a second rare earth oxide including ytterbia, a third rare
earth oxide including samaria, and a fourth rare earth oxide
including at least one of lutetia, scandia, ceria, neodymia,
europia, and gadolinia, where the second layer includes a columnar
microstructure; and depositing a third plurality of particles using
a suspension plasma spray technique to form a third layer on the
second layer, where the third plurality of particles includes a
third base oxide including zirconia or hafnia, the second rare
earth oxide, the third rare earth oxide, and a fifth rare earth
oxide including at least one of lutetia, scandia, ceria, neodymia,
europia, and gadolinia, where the third layer has a dense
microstructure and has a lower porosity than the second layer.
[0007] The details of one or more examples are set forth in the
accompanying drawings and the description below. Other features,
objects, and advantages will be apparent from the description and
drawings, and from the claims.
BRIEF DESCRIPTION OF DRAWINGS
[0008] FIG. 1A is a schematic diagram illustrating an example
system for forming an article that includes a multi-layer TBC on a
substrate using a suspension plasma spray technique.
[0009] FIG. 1B is an enlarged cross-sectional view of the example
article from FIG. 1A that includes a multi-layer TBC formed on
substrate.
[0010] FIG. 2 is a cross-sectional diagram of an example article
that includes a multi-layer TBC deposited on a bond coat and a
substrate using a suspension thermal spray technique.
[0011] FIG. 3 is a cross-sectional diagram of another example
article that includes a multi-layer TBC deposited on a substrate
using a suspension thermal spray technique.
[0012] FIG. 4 is a flow diagram illustrating an example technique
for depositing a layer on a substrate using suspension plasma
spray.
[0013] FIG. 5 is a flow diagram illustrating an example technique
for depositing a multi-layer TBC on a substrate using a suspension
plasma spray technique.
DETAILED DESCRIPTION
[0014] The disclosure describes articles including a multi-layer
thermal barrier coating (TBC) formed using suspension plasma spray
techniques and techniques of forming the same. In some examples,
TBCs may have a low thermal conductivity to reduce the transfer of
thermal energy from the high-temperature gases to the substrate.
However, erosion and contamination can reduce the life of TBCs,
which may make the TBC less effective at protecting the underlying
substrate. Erosion and/or contamination may occur when deleterious
environmental species, such as, for example, calcium magnesium
aluminum silicate (CMAS), penetrate the TBC. The presence of a
deleterious environmental species in the TBC may weaken or degrade
the TBC layers, causing damage to an underlying substrate due to
stresses imposed on the TBC during thermal cycling within the
high-temperature operational environments. For example, CMAS may
migrate into the layers of the TBC, reducing the insulative
properties of the layer and/or physically stressing the TBC layer
leading to spallation. Additionally, or alternatively, the CMAS may
migrate through the TBC into underlying layers or to the underlying
substrate, leading to unwanted side reactions.
[0015] A TBC with a dense microstructure may help prevent some of
the deleterious environmental species from migrating into the TBC
and causing degradation of the TBC, or may help prevent deleterious
environmental species from migrating to other layers or the
substrate and causing additional degradation of the article.
However, a TBC with only a dense microstructure may be subject to
increased in-plane strain during thermal cycling, such as, for
example, in a high-temperature gas turbine engine. A TBC with only
a dense microstructure also may exhibit increased thermal
conductivity making the TBC less effective.
[0016] In some examples, improved thermal cycling performance of
the TBC may be obtained with a TBC having a predominately columnar
microstructure. A columnar microstructure may include columns of
the coating material extending from the surface of a substrate with
elongated intercolumnar voids that have a crystallographic texture.
A columnar microstructure may allow for the TBC to have improved
in-plane strain tolerance and a decreased thermal conductivity.
However, a columnar microstructure may be less durable due to the
increased porosity. Traditional deposition techniques, such as, for
example, electron beam-physical vapor deposition (EB-PVD), may be
capable of producing such columnar microstructures. However, EB-PVD
may be complex, expensive, limited by the number of manufacturing
sites with EB-PVD technology, and may have poor process efficiency,
such as, for example, less than 10% efficiency in deposition of raw
materials. Further, EB-PVD processes may not allow for deposition
of multi-layer coatings including more than one microstructure or
phase constituents.
[0017] As described herein, one or more layers of the multi-layer
TBC may be deposited on a substrate using a suspension plasma spray
technique. The suspension plasma spray technique may be used to
form a multi-layer TBC having at least two different
microstructures, such as, for example, at least one layer with a
dense microstructure and at least one layer with a columnar
microstructure to provide synergistic properties to the resultant
TBC. For example, the multi-layer structure of the TBC may help
prevent deleterious environmental species from migrating into the
TBC or to the substrate, as well as provide improved thermal
cycling performance of the TBC.
[0018] In some examples, the suspension plasma spray techniques
described herein may be used to deposit a relatively small particle
coating material (e.g., average particle size less than about 1
.mu.m to about 25 .mu.m, or less than about 1 .mu.m to about 10
.mu.m) in order to obtain a selected coating microstructure (e.g.,
dense or columnar). As used herein, "average particle diameter,"
"average diameter," or "particle size" may be an equivalent mean
diameter (e.g., if the particles are not spherical) of a given
particle size distribution.
[0019] Such particle sizes may be insufficient for deposition by
traditional thermal spray techniques, such as plasma spray
techniques, which typically utilize a minimal particle size of
about 30-60 .mu.m to avoid agglomeration or fouling of the thermal
spray device. Additionally, the suspension plasma spray techniques
may provide a more efficient and cost-effective way of producing
the multi-layer TBC compared to vapor deposition techniques (e.g.,
EB-PVD).
[0020] FIG. 1A is a schematic diagram illustrating an example
system 10 for forming an article 40 that includes a multi-layer TBC
18 on a substrate 16 using a suspension plasma spray technique.
System 10 includes a chamber 12 that encloses a stage 14 configured
to receive substrate 16, a suspension source 22, a plasma spray
device 20 that receives a suspension 26 (e.g., coating material 28
suspended in carrier 30) from suspension source 22, and a computing
device 24 configured to control the feed of suspension 26 from
suspension source 22 to thermal spray device 20 and the subsequent
deposition of coating material 28 to form multi-layer TBC 18 on
substrate 16.
[0021] In some examples, article 40 may include a component of a
gas turbine engine. For example, article 40 may include a part that
forms a portion of a flow path structure, a seal segment, a blade
track, an airfoil, a blade, a vane, a combustion chamber liner, or
another portion of the gas turbine engine. FIG. 1B is an enlarged
cross-sectional view of the example article 40 from FIG. 1A that
includes multi-layer TBC 18 on substrate 16 using system 10. As
used herein, "formed on" and "on" means a layer or coating that is
formed on top of another layer or coating and encompasses both a
first layer or coating formed immediately adjacent a second layer
or coating and a first layer or coating formed on top of a second
layer or coating with one or more intermediate layers or coatings
present between the first and second layers or coatings. In
contrast, "formed directly on" and "directly on" denote a layer or
coating that is formed immediately adjacent to another layer or
coating, i.e., there are no intermediate layers or coatings. In
some examples, as shown in FIG. 1B, multi-layer TBC 18 may be
directly on substrate 16.
[0022] Substrate 16 may include a material suitable for use in a
high-temperature environment. In some examples, substrate 16
includes a super alloy including, for example, an alloy based on
Ni, Co, Ni/Fe, or the like. In examples where substrate 16 includes
a super alloy material, substrate 16 may also include one or more
additives such as titanium (Ti), cobalt (Co), or aluminum (Al),
which beneficially affect the mechanical properties of substrate 16
including, for example, toughness, hardness, temperature stability,
corrosion resistance, oxidation resistance, or the like.
[0023] In some examples, substrate 16 may include a ceramic or a
ceramic matrix composite (CMC). Suitable ceramic materials, may
include, for example, a silicon-containing ceramic, such as silica
(SiO.sub.2), silicon carbide (SiC); silicon nitride
(Si.sub.3N.sub.4); alumina (Al.sub.2O.sub.3); an aluminosilicate; a
transition metal carbide (e.g., WC, Mo.sub.2C, TiC); a silicide
(e.g., MoSi.sub.2, NbSi.sub.2, TiSi.sub.2); combinations thereof;
or the like. In some examples in which substrate 16 includes a
ceramic, the ceramic may be substantially homogeneous.
[0024] In examples in which substrate 16 includes a CMC, substrate
16 may include a matrix material and a reinforcement material. The
matrix material may include, for example, silicon metal or a
ceramic material, such as silicon carbide (SiC), silicon nitride
(Si.sub.3N.sub.4), an aluminosilicate, silica (SiO.sub.2), a
transition metal carbide or silicide (e.g., WC, Mo.sub.2C, TiC,
MoSi.sub.2, NbSi.sub.2, TiSi.sub.2), or other ceramics described
herein. The CMC may further include a continuous or discontinuous
reinforcement material. For example, the reinforcement material may
include discontinuous whiskers, platelets, fibers, or particulates.
Additionally, or alternatively, the reinforcement material may
include a continuous monofilament or multifilament two-dimensional
or three-dimensional weave. In some examples, the reinforcement
material may include carbon (C), silicon carbide (SiC), silicon
nitride (Si.sub.3N.sub.4), an aluminosilicate, silica (SiO.sub.2),
a transition metal carbide or silicide (e.g. WC, Mo.sub.2C, TiC,
MoSi.sub.2, NbSi.sub.2, TiSi.sub.2), another ceramic material
described herein, or the like.
[0025] In some examples, the composition of the reinforcement
material is the same as the composition of the matrix material. For
example, a matrix material including silicon carbide may surround a
reinforcement material including silicon carbide whiskers or
fibers. In other examples, the reinforcement material includes a
different composition than the composition of the matrix material,
such as aluminosilicate fibers in an alumina matrix, or the like.
In some examples, substrate 16 that includes a CMC comprising a
reinforcement material of silicon carbide fibers embedded in a
matrix material of silicon carbide. In some examples, substrate 16
includes a SiC--SiC CMC.
[0026] Multi-layer TBC 18 may be deposited on substrate 16 using
the suspension plasma spray techniques of the present disclosure.
Multi-layer TBC 18 may reduce the transfer of thermal energy from
high-temperature gases to substrate 16; help prevent deleterious
environmental species (e.g., CMAS) from migrating into the layers
of TBC 18, any optional underlying layers, or substrate 16; provide
erosion resistance; improve thermal cycling performance of article
40; or combinations thereof.
[0027] Multi-layer TBC 18 includes a first layer 42, a second layer
44, and a third layer 46. Each layer of multi-layer TBC 18 may
contribute to properties of multi-layer TBC 18, and each layer may
be selected independently to provide similar or different
properties to multi-layer TBC 18. For example, first layer 42 may
provide improved thermal cycling performance, second layer 44 may
provide a low thermal conductivity, and third layer 46 may improve
erosion resistance and/or CMAS resistance.
[0028] First layer 42 includes a first base oxide of either
zirconia or hafnia and a first rare earth oxide of yttria deposited
in a columnar microstructure on substrate 16. For example, first
layer 42 may include yttria-stabilized zirconia or hafnia, that
includes predominately (e.g., the main component or a majority) of
the first base oxide zirconia (ZrO.sub.2) or hafnia (HfO.sub.2)
mixed with a minority amount of yttria (Y.sub.2O.sub.3). In some
examples, the first base oxide may consist of zirconia. The use of
the terms "first," "second," "third," etc. oxide is used in an
ordinal sense to identify and distinguish among the different oxide
components of the various layers rather than in the cardinal sense
to limit or imply the total number of oxides that may be present
within a respective layer.
[0029] In some examples, first layer 42 may consist essentially of
zirconia and yttria. As used herein, to "consist essentially of"
means to consist of the listed element(s) or compound(s), while
allowing the inclusion of impurities present in small amounts such
that the impurities do no substantially affect the properties of
the listed element or compound. For example, the purification of
many rare earth elements may be difficult, and thus the nominal
rare earth element may include small amounts of other rare earth
elements. This mixture is intended to be covered by the language
"consists essentially of." In some examples, first layer 42 may
consist essentially of yttria-stabilized-zirconia, which includes
about 92 weight percent (wt. %) to about 94 wt. % of the base oxide
zirconia stabilized by about 6 wt. % to about 8 wt. % of the rare
earth oxide yttria.
[0030] In some examples, having first layer 42 consist essentially
of zirconia and yttria may improve the layer's thermal cycling
resistance (e.g., a long thermal cycling life), and/or adhesion to
underlying substrate 16 or an optional bond coat. For example,
first layer 42 consisting essentially of zirconia and yttria may
reduce the coefficient of thermal expansion of the layer such that
it is more comparable to that of substrate 16. Additionally, or
alternatively, the overall high purity of first layer 42 (e.g.,
compared to the purity of second layer 44 which may include
additional oxides) may reduce the chance of side reactions or
coefficient of thermal expansion mismatches within the layer to
provide better long-term adhesion between first layer 42 and
substrate 16.
[0031] First layer 42 may have a coefficient of thermal expansion
that lies between that of substrate 16 and second layer 44. In this
way, the coefficient of thermal expansion mismatch may be reduced
due to first layer 42 acting as an intermediate or gradient layer
between substrate 16 and second layer 44. In turn, first layer 42
may reduce stress due to thermal expansion between substrate 16 and
second layer 44 to improve the working life of article 40.
[0032] In some examples, first layer 42 may be deposited on
substrate 16 using the suspension plasma spray techniques of the
present disclosure. The suspension plasma spray techniques may
allow the resultant first layer 42 to have a substantially columnar
microstructure that provides improved thermal cycling performance
by reducing the in-plane strain exerted between substrate 16 and
first layer 42 during thermal cycling in comparison to a comparable
layer that does not possess a columnar microstructure.
[0033] As described further below, the columnar microstructure of
first layer 42 may be obtained using system 10 to spray deposit a
coating material 28 that includes very fine particles (e.g.,
average particle size less than about 1 .mu.m) of the base oxide
(e.g., zirconia) and rare earth oxide yttria. As used herein, "very
fine particles" is intended to describe particles with an average
particle diameter of less than about 1 .mu.m. During the suspension
plasma spray process, the very fine particles of coating material
28 may be carried by the plasma stream of plasma spray device 20 to
be deposited on substrate 16. Due to the small particle size,
coating material 28 is more likely to be deflected within the
plasma stream as the stream contacts the surface of substrate 16.
The deflection causes the very fine particles of coating material
28 to deposit on substrate 16 at angles other than normal to the
surface of substrate 16. This process allows coating material 28 to
be deposited with the formation of columns within the
microstructure, which may otherwise not be possible with larger
particle sizes (e.g., greater than 1 .mu.m). For example, coating
material 28 may follow trajectories of the plasma stream as the
stream contacts the surface of substrate 16 and deflects
horizontally along the surface of substrate 16. In turn, as coating
material 28 is deposited, the deposits form asperities creating
shadows downstream of the trajectory of coating material 28 in the
plasma stream. In some such examples, coating material 28 may not
deposit in at least some of the shadows, resulting in the formation
the intercolumnar voids of the columnar microstructure. The
columnar microstructure of first layer 42 may provide increased
in-plane strain tolerance and improved thermal cycling resistance,
resulting in better adhesion properties and a more robust article
40.
[0034] In other examples, first layer 42 may be deposited using
techniques other than the suspension plasma spray techniques
described herein including, for example, traditional thermal
spraying, including, air plasma spraying, high velocity oxy-fuel
(HVOF) spraying, low vapor plasma spraying; physical vapor
deposition (PVD), including EB-PVD, directed vapor deposition
(DVD), and cathodic arc deposition; chemical vapor deposition
(CVD); slurry process deposition; sol-gel process deposition;
electrophoretic deposition; or the like. In the case in which first
layer 42 is deposited using an alternative deposition technique,
first layer 42 may still include a substantially columnar
microstructure. However, compared to some alternative techniques
(e.g., EB-PVD) the suspension plasma spray techniques described
herein may demonstrate a higher conversion yield of the raw
materials into the coating layer (e.g., an efficiency of more than
about 50% as compared to an efficiency of about 10% associated with
EB-PVD).
[0035] In some examples, first layer 42 may be a relatively thin
layer. For example, first layer 42 may be between about 0.0005
inches and about 0.003 inches (e.g., between about 10 .mu.m and
about 80 .mu.m). Even at these relatively small thicknesses, first
layer 42 may contribute to thermal cycling performance of
multi-layer TBC 18.
[0036] Second layer 44 may include a second base oxide of zirconia
or hafnia and at least one rare earth oxide, such as, for example,
oxides of Lu, Yb, Tm, Er, Ho, Dy, Gd, Tb, Eu, Sm, Pm, Nd, Pr, Ce,
La, Y, Sc, and combinations thereof, on first layer 42 with a
columnar microstructure. Second layer 44 may include predominately
(e.g., the main component or a majority) the base oxide zirconia or
hafnia mixed with a minority amounts of the at least one rare earth
oxide.
[0037] In some examples, second layer 44 may include the second
base oxide and a second rare earth oxide including ytterbia, a
third rare earth oxide including samaria, and a fourth rare earth
oxide including at least one of lutetia, scandia, ceria, neodymia,
europia, and gadolinia. In some examples, the fourth rare earth
oxide may include gadolinia such that the second layer 44 may
include the second base oxide (e.g., zirconia), ytterbia, samaria,
and gadolinia deposited on first layer 42 with a columnar
microstructure. Second layer 44 may include predominately (e.g.,
the main component or a majority) the second base oxide (e.g.,
zirconia) mixed with a minority amounts of ytterbia, gadolinia, and
samaria. The below description of second layer 44 is primarily
described with respect to the second base oxide including zirconia
and the second, third, and fourth rare earth oxides including
ytterbia, gadolinia, and samaria, however in other examples, other
rare earth oxides may be used and/or hafnia may be used as the
second base oxide.
[0038] In some examples, the composition (e.g., zirconia, ytterbia,
gadolinia, and samaria) and the columnar microstructure of second
layer 44 may provide improved thermal insulation and protection to
substrate 16 from high temperatures, e.g., high-temperature of the
turbine gas compared to other coating compositions or
microstructures. For example, during operation of article 40 in a
high temperature environment, heat is transferred through
multi-layer TBC 18 through conduction and radiation. The inclusion
of one or more rare earth oxides, such as ytterbia, gadolinia, and
samaria within a layer of predominately zirconia may help decrease
the thermal conductivity of second layer 44. While not wishing to
be bound by any specific theory, the inclusion of ytterbia,
gadolinia, and samaria in second layer 44 may reduce thermal
conductivity through one or more mechanisms, including phonon
scattering due to point defects and grain boundaries in the
zirconia crystal lattice due to the rare earth oxides, reduction of
sintering, and porosity.
[0039] The composition of second layer 44 may be selected to
provide a desired phase constitution. Accessible phase
constitutions include tetragonal prime (t'), cubic, and compound
RE.sub.2O.sub.3--ZrO.sub.2 or RE.sub.2O.sub.3--HfO.sub.2 (where RE
is a rare earth element) phase constitutions measured using x-ray
diffraction. Second layer 44 may include tetragonal prime (t'),
cubic, or compound phase constitutions or combinations thereof.
[0040] For example, to achieve a compound phase constitution, a
layer may include about 20 mol. % to about 40 mol. % ytterbia,
about 10 mol. % to about 20 mol. % gadolinia, about 10 mol. % to
about 20 mol. % samaria, and the balance the respective base oxide
(e.g., zirconia or hafnia) and any impurities present.
[0041] To achieve a cubic phase constitution, a layer may include
about 3 mol. % to about 10 mol. % ytterbia, about 1 mol. % to about
5 mol. % gadolinia, about 1 mol. % to about 5 mol. % samaria, and
the balance the respective base oxide (e.g., about 80 mol. % to
about 95 mol. % zirconia or hafnia) and any impurities present.
[0042] To achieve a tetragonal prime phase constitution, a layer
may include about 1 mol. % to about 5 mol. % ytterbia, about 0.1
mol. % to about 3 mol. % gadolinia, and about 0.1 mol. % to about 3
mol. % samaria, and the respective base oxide (about 89 mol. % to
about 98.8 mol. % zirconia or hafnia) and any impurities
present.
[0043] In some examples, second layer 44 may include or include a
majority of a cubic phase constitution (e.g., the majority of
second layer 44 consists of a cubic phase constitution). In some
examples, second layer 44 may consist essentially of a cubic phase
constitution. The cubic phase constitution may provide second layer
44 with a lower thermal conductivity than a layer having a similar
composition, but with a tetragonal prime or a compound phase
constitution.
[0044] In some examples, second layer 44 may include ytterbia in a
concentration of between about 3 mol. % and about 10 mol. %,
gadolinia in a concentration between about 1 mol. % and about 5
mol. %, samaria in a concentration between about 1 mol. % and about
5 mol. %, and the balance zirconia and any impurities present in a
cubic phase constitution. In some examples, second layer 44 may
include ytterbia in a concentration of between about 3.5 mol. % and
about 4.5 mol. % (e.g., about 4 mol. %), gadolinia in a
concentration between about 2.5 mol. % and about 3.5 mol. % (e.g.,
about 3 mol. %), samaria in a concentration between about 2.5 mol.
% and about 3.5 mol. % (e.g., about 4 mol. %), and the balance
zirconia (e.g., about 88.5 mol. % to about 91.5 mol. %) and any
impurities present in a cubic phase constitution.
[0045] In some examples, the inclusion of ytterbia, gadolinia, and
samaria in second layer 44 may also provide second layer 44 with
increased resistance to CMAS degradation compared by
yttria-stabilized zirconia, reduce the thermal conductivity of
second layer 44, or both. Although the composition of second layer
44 is described with respect to zirconia, ytterbia, gadolinia, and
samaria, one or more of the zirconia, ytterbia, gadolinia, and
samaria may be replaced by one or more of hafnia or a rare earth
oxide, such as, for example, oxides of Lu, Yb, Tm, Er, Ho, Dy, Gd,
Tb, Eu, Sm, Pm, Nd, Pr, Ce, La, Y, or Sc.
[0046] As with first layer 42, the suspension plasma spray
techniques described herein may be used to deposit second layer 44
on first layer 42. For example, system 10 may be used to deposit a
very fine particle coating material 28 (e.g., average particle size
less than about 1 .mu.m) having the compositional makeup of second
layer 44 to form second layer 44 with a columnar microstructure. As
described above, coating material 28 with very fine particle sizes
may be used to generate the columnar microstructure which may
otherwise not be obtained using traditional thermal spray
techniques. The use of very fine particles with the suspension
plasma spray techniques as described herein may result in second
layer 44 including a substantially columnar microstructure that
provides improved thermal cycling performance and thermal
insulative properties in comparison to other layers that do not
possess a columnar microstructure.
[0047] In some examples, second layer 44 may have a thickness of
between about 0.001 inches and about 0.03 inches (e.g., between
about 25 .mu.m and about 7650 .mu.m). For example, second layer 44
may be between about 0.004 inches and about 0.015 inches (e.g.,
between about 100 .mu.m and about 380 .mu.m).
[0048] Multi-layer TBC 18 also includes third layer 46, which may
exhibit a relatively dense microstructure. The relatively dense
microstructure may reduce or substantially prevent exposure of
substrate 16 to deleterious environmental species (e.g., CMAS),
prevent deterioration and erosion of multi-layer TBC 18, and
increase the service life of substrate 16.
[0049] Third layer 46 may include a third base oxide of zirconia or
hafnia and at least one rare earth oxide, such as, for example,
oxides of Lu, Yb, Tm, Er, Ho, Dy, Gd, Tb, Eu, Sm, Pm, Nd, Pr, Ce,
La, Y, Sc, and combinations thereof, on second layer 44 with a
dense microstructure. Third layer 46 may include predominately
(e.g., the main component or a majority) the third base oxide of
zirconia or hafnia mixed with a minority amounts of the at least
one rare earth oxide.
[0050] In some examples, third layer 46 may include the third base
oxide and the second rare earth oxide including ytterbia, the third
rare earth oxide including samaria, and a fifth rare earth oxide
including at least one of lutetia, scandia, ceria, neodymia,
europia, and gadolinia. In some examples, the fifth rare earth
oxide may include gadolinia such that third layer 46 may include
predominately (e.g., the main component or a majority) the third
base oxide (e.g., zirconia) mixed with a minority amounts of
ytterbia, gadolinia, and samaria on second layer 44 in a dense
microstructure. The below description of third layer 44 is
primarily described with respect to the layer including zirconia
and the rare earth oxides ytterbia, gadolinia, and samaria, however
in other examples, other rare earth oxides may be used and/or
hafnia may be used as the third base oxide.
[0051] As used herein, a "dense microstructure" may be
characterized by a layer with a relatively low resultant volume
porosity (e.g., a porosity of less than about 5 percent by volume
(vol. %)). In other examples, third layer 46 may have a porosity
greater than about 5 vol. %, such as for example a porosity of less
than about 20 vol. %, such as less than about 15 vol. %, or less
than about 10 vol. %. In some examples, second layer 44 may have
first porosity, and third layer 46 may have a second porosity, and
the second porosity of third layer 46 may be less than the first
porosity of second layer 44. The porosity of deposited third layer
46 may be measured as a percentage of pore volume divided by total
volume of the layer, and may be measured using optical microscopy
or mercury porosimetry. In some examples, the porosity of third
layer 46 may be measured using ASTM B328-94. The relatively low
level of porosity may reduce the migration of deleterious elements
(e.g., CMAS) through third layer 46 that may otherwise damage or
degrade substrate 16, other layers included in multi-layer TBC 18,
or other layers within article 40. Additionally, or alternatively,
the composition of third layer 46 and the relatively low porosity
may improve the durability of the layer and article 40. The
relatively low porosity of third layer 46 may also improve the
erosion resistance of third layer 46.
[0052] The composition of third layer 46 may be selected to provide
one or more desired phase constitutions, as described above with
respect to second layer 44. In some examples, third layer 46 may
include or include a majority of a tetragonal prime phase
constitution. In some examples, third layer 46 may include ytterbia
in a concentration of between about 1 mol. % and about 5 mol. %,
gadolinia in a concentration between about 0.1 mol. % and about 3
mol. %, samaria in a concentration between about 0.1 mol. % and
about 3 mol. %, and the balance zirconia (e.g., about 89 mol. % to
about 98.8 mol. %) and any impurities present in the phase
constitution. In some examples, third layer 46 may include ytterbia
in a concentration of between about 2 mol. % and about 4 mol. %
(e.g., about 2.5 mol. %), gadolinia in a concentration between
about 0.1 mol. % and about 2 mol. % (e.g., about 1 mol. %), samaria
in a concentration between about 0.1 mol. % and about 1 mol. %
(e.g., about 0.5 mol. %), and the balance zirconia and any
impurities present in a tetragonal prime phase constitution.
[0053] In some examples, the zirconia, ytterbia, gadolinia, and
samaria present in the third layer 46 may consist essentially of a
tetragonal prime phase constitution. Although the composition of
third layer 46 is described with respect to zirconia, ytterbia,
gadolinia, and samaria, one or more of the zirconia, ytterbia,
gadolinia, and samaria may be replaced by one or more of hafnia or
a rare earth oxide, such as, for example, oxides of Lu, Yb, Tm, Er,
Ho, Dy, Gd, Tb, Eu, Sm, Pm, Nd, Pr, Ce, La, Y, or Sc.
[0054] In some examples, a layer including a tetragonal prime phase
constitution may have improved thermal cycling resistance and/or
durability in comparison to a layer including a cubic phase
constitution, but generally exhibits a higher thermal conductivity
than a comparable layer including a cubic phase constitution. Thus,
by forming TBC 18 with second layer 44 having a columnar
microstructure and substantially cubic phase constitution of
zirconia, ytterbia, gadolinia, and samaria and third layer 46 with
a dense microstructure and substantially tetragonal prime phase
constitution of zirconia, ytterbia, gadolinia, and samaria, the two
layers may provide multi-layer TBC 18 with low thermal
conductivity, improved thermal cycling resistance, and improved
overall durability.
[0055] In some examples, third layer 46 may be deposited with a
dense microstructure using the suspension plasma spray techniques
described herein. For example, by controlling one or more of the
deposition parameters of the suspension plasma spray techniques,
coating material 28 may be deposited as relatively dense
microstructure with low porosity. One parameter that may affect the
resultant microstructure of the deposited layer is the particle
size of coating material 28. For example, coating material 28
including a fine particle (e.g., between about 1 .mu.m and about 25
.mu.m) may result in third layer 46 with a dense microstructure. As
used herein, "fine particle" is intended to describe particles with
an average particle diameter between about 1 .mu.m and about 25
.mu.m. The fine particles of coating material 28 (e.g., in
comparison to other deposition techniques) may permit a more
compressed arrangement of the deposited particles resulting in
third layer 46 with a reduced porosity, reduced pore size, higher
density, or combinations thereof. The increased density of third
layer 46 may help prevent exposure of the surface of a substrate to
deleterious environmental species, prevent deterioration and
erosion of multi-layer TBC 18, and increase the service life of
substrate 16.
[0056] In some examples, the size of the pores that are present in
third layer 46 may be smaller than pores generated using other
thermal spray techniques. For example, due to the particle size
associated with traditional plasma spray techniques (e.g., particle
diameters on the order of about 30-60 .mu.m), the resultant pores
produced between the deposited particles will remain relatively
large due to the geometric size and shape of the deposited
particles. Because the suspension plasma spray techniques described
herein can be used to deposit relatively small size particles
(e.g., particle diameters less than about 25 .mu.m), the pores
between the deposited particles may likewise be reduced in size.
The reduced pore size may result in the pores between deposited
particles to be less likely to be interconnected within the
thickness of third layer 46. In some examples, pores of third layer
46 may be on the order of about 1 .mu.m to about 10 .mu.m. The
smaller pore size of third layer 46 may reduce migration of
deleterious compounds, e.g., CMAS, through third layer 46.
Additionally, or alternatively, the smaller pore size may provide
phonon scattering, increased difficulty of heat transfer though
third layer 46, and/or a decreased thermal conductivity of third
layer 46.
[0057] Additionally, or alternatively, the suspension plasma spray
techniques described herein may help reduce the overall production
cost and time for forming multi-layer TBC 18. For example, using
traditional techniques, multi-layer TBC 18 may have to be deposited
using multiple techniques, such as, for example, conventional
plasma spraying and EB-PVD, in order to obtain multi-layer TBC 18
with more than one microstructure, e.g., second layer 44 with a
columnar microstructure and third layer 46 with a dense
microstructure. Using the suspension plasma spray techniques of the
present disclosure, process parameters may be adjusted to influence
the microstructure of the resultant layer of multi-layer TBC
18.
[0058] In some examples, third layer 46 may have a thickness of
between about 0.001 inches and about 0.005 inches (e.g., between
about 25 .mu.m and about 130 .mu.m).
[0059] In some examples, third layer 46 may further include alumina
(Al.sub.2O.sub.3). The presence of alumina in third layer 46 may
improve the durability and toughness of third layer 46.
Additionally, or alternatively, the presence of alumina in third
layer 46 may provide enhanced erosion and contamination resistance
of multi-layer TBC 18 compared to some TBCs that do not include a
layer including alumina. For example, including of alumina may
reduce a reaction rate with alumina components in CMAS.
[0060] In examples in which third layer 46 includes alumina, the
layer may include at least two distinct phase constitutions
including a first phase including the third base oxide (e.g.,
zirconia), the second rare earth oxide (e.g., ytterbia), the third
rare earth oxide (e.g., samaria), and the fifth rare earth oxide
(e.g., gadolinia) (e.g., a tetragonal prime phase constitution) and
a second phase including alumina. The presence of more than one
phase may help enhance the creep strength of third layer 46
compared to a single-phase layer, which in turn, may increase the
durability and useful life of third layer 46 and multi-layer TBC
18.
[0061] In some examples, the predominate phase (e.g., present at
more than 50 vol. %) of the third layer 46 may include the third
base oxide (e.g., zirconia), the second rare earth oxide (e.g.,
ytterbia), the third rare earth oxide (e.g., samaria), and the
fifth rare earth oxide (e.g., gadolinia). Depending on the
composition of third layer 46, the alumina may be present as a
second phase dispersed within the first phase. For example, the
first phase may be a substantially continuous throughout third
layer 46 (e.g., the first phase material remains connected
throughout third layer 46) with discrete second phase regions of
alumina included within the substantially continuous first
phase.
[0062] In some examples, third layer 46 including alumina may
include a boundary region between the first phase including the
third base oxide (e.g., zirconia), the second rare earth oxide
(e.g., ytterbia), the third rare earth oxide (e.g., samaria), and
the fifth rare earth oxide (e.g., gadolinia) and the second phase
including the alumina. The boundary region between the first and
second phases may include a reaction product from a reaction
between the oxides of the first phase and the alumina of the second
phase or may include a different crystal structure where the
alumina alloys with, e.g., the zirconia, ytterbia, gadolinia, and
samaria. Alternatively, or in addition, the optional alumina of
third layer 46 may be alloyed throughout the phase including the
third base oxide (e.g., zirconia), the second rare earth oxide
(e.g., ytterbia), the third rare earth oxide (e.g., samaria), and
the fifth rare earth oxide (e.g., gadolinia).
[0063] In some examples, the first phase may include a tetragonal
prime phase constitution with ytterbia in a concentration between
about 2 mol. % and about 4 mol. % (e.g., about 2.5 mol. %),
gadolinia in a concentration between about 0.1 mol. % and about 2
mol. % (e.g., about 1 mol. %), samaria in a concentration between
about 0.1 mol. % and about 1 mol. % (e.g., about 0.5 mol. %), and
the and the balance the third base oxide (e.g., zirconia) and any
impurities present. The second phase of third layer 46 may include
or consist essentially of alumina. Third layer 46 may include
between about 10 mol. % and about 50 mol. % alumina. For example,
third layer 46 may include between about 10 mol. % and about 50
mol. % alumina, between about 10 mol. % and about 30 mol. %
alumina, or between about 10 mol. % and about 20 mol. % alumina.
The two phases may be deposited as third layer 46 using the
suspension plasma spray deposition techniques described herein by,
for example, pre-mixing particles of the alumina phase and
pre-alloyed tetragonal prime phase constitutions together in
suspension 26.
[0064] Returning to FIG. 1A, system 10 may be used to apply one or
more layers of multi-layer TBC 18 to substrate 16 using a
suspension plasma spray technique. Chamber 12 may substantially
enclose (e.g., enclose or nearly enclose) stage 14 that receives
substrate 16, and plasma spray device 20. In some examples, stage
14 may be configured to selectively position and restrain substrate
16 in place relative to plasma spray device 20 during formation of
multi-layer TBC 18. For example, stage 14 may be translatable
and/or rotatable along at least one axis to position substrate 16
relative to plasma spray device 20 to facilitate the application of
multi-layer TBC 18 on substrate 16 via plasma spray device 20.
[0065] System 10 also includes suspension source 22 configured to
deliver a suspension 26 including a coating material 28 (e.g., the
solid materials that form one of the layers of multi-layer TBC 18)
and a carrier 30 to plasma spray device 20 or a plume generated by
plasma spray device 20. In some examples, suspension source 22 may
include a nozzle or other apparatus within chamber 12 for
introducing suspension 26 to plasma spray device 20 or a plume
generated by plasma spray device 20. Suspension source 22 may be
communicatively coupled to computing device 24, such that computing
device 24 may control suspension source 22 (e.g., opening or
closing a valve, positioning suspension source 22, controlling a
flow rate of suspension 26 from suspension source 22 to plasma
spray device 20, or the like).
[0066] Coating material 28 may include a particle form of the
respective materials used to form first layer 42, second layer 44,
and third layer 46 of multi-layer TBC 18. For example, coating
material 28 may include zirconia and yttria to deposit first layer
42; zirconia, ytterbia, gadolinia, and samaria to deposit second
layer 44; or zirconia, ytterbia, gadolinia, samaria, and optionally
alumina, to deposit third layer 46, as described above. Coating
material 28 may be in the form of particles to facilitate softening
or vaporization of coating material 28 by a heated plume created by
plasma spray device 20. In some examples, coating material 28 may
include separate coating materials for each respective layer of
first layer 42, second layer 44, and third layer 46.
[0067] In some examples, coating material 28 may include a single
particle type, e.g., a pre-alloyed particle with the desired
composition and/or phase constitution. The single particle type may
allow for a uniform disbursement and control the composition and/or
phase constitution of the resultant layer of multi-layer TBC 18.
The pre-alloyed particles may include a desired phase constitution
for the layer to be deposited, e.g., cubic or tetragonal prime
phase constitutions. In other examples, coating material 28 may
include discrete particles, e.g., distinct particles of each of the
base oxide, rare earth oxides, and alumina (where used) combined to
make up the composition of the respective layer of multi-layer TBC
18. The particle materials may be mechanically premixed within
suspension 26 prior to deposition. Due to the relatively small
particle size used in the suspension plasma spray techniques, the
discrete particles may intimately mix during the deposition process
to form the desired phase constitution.
[0068] In some examples, coating material 28 may have a very fine
particle size, which may result in deposition of a layer with a
columnar microstructure. As described above, the very fine particle
diameter sizes may allow for vaporization of at least some of the
particles and may allow for coating material 28 to be deflected
within the plasma stream, causing coating material 28 to deposit on
substrate 16 at angles other than normal to the surface of
substrate 16 and resulting in a layer with a columnar
microstructure. In some examples, the particle size of coating
material 28 for creating the columnar microstructure may define an
average particle diameter between about 0.01 .mu.m and about 1
.mu.m, between about 0.01 .mu.m and about 0.5 .mu.m, or between
about 0.01 .mu.m and about 0.05 .mu.m.
[0069] In other examples, coating material 28 may be deposited as a
layer including a dense microstructure (e.g., third layer 46). In
some examples, the average particle diameter for producing a layer
with a dense microstructure may still remain relatively small
(e.g., an average particle diameter less than about 25 .mu.m, less
than about 10 .mu.m, or less than about 1 .mu.m) compared to
particle sizes used with traditional plasma spray techniques. In
some examples, the particles sizes may be similar to the particles
sizes used to form a columnar microstructure but may result in a
dense microstructure by modifying the deposition parameters, such
as, for example, the spraying distance and/or power, of system 10.
For example, decreasing the spraying distance, decreasing the
suspension feed rate, and/or increasing the power may result in a
dense microstructure even when relatively small particles are used.
In some examples, the dense microstructure obtained by the
suspension plasma spray techniques described herein may allow for a
layer of multi-layer TBC 18 to exhibit a decreased overall porosity
and resultant higher density compared to a comparable layer
deposited using traditional thermal spray techniques.
[0070] Suspension 26 also includes carrier 30 that acts as a
carrier fluid and allows small particles (e.g., less than about 25
.mu.m or less than about 10 .mu.m) of coating material 28 to be
used without agglomeration of the particles prior to deposition. In
some examples, carrier 30 may be a water-based or alcohol-based
solvent. Examples of suitable materials for carrier 30 may include,
for example, water, ethanol, methanol, isopropyl alcohol, or the
like.
[0071] Coating material 28 may be added to carrier 30 to form
suspension 26. In some examples, suspension 26 may include may
include about 1 vol. % to about 30 vol. % solid loading of coating
material 28 in carrier 30. In some examples, coating material 28
may be added to carrier 30 to form suspension 26 with a desired
viscosity, stability of the colloidal suspension, e.g.,
flocculation, heat capacity, or any other parameter to fit the
needs of system 10. In some examples, suspension 26 may include a
combustible liquid that may undergo an exothermic reaction upon
spraying.
[0072] In some examples, suspension 26 may further include one or
more delivery aids (e.g., additives that do not form multi-layer
TBC 18 but aid in the delivery or deposition of coating material 28
within carrier 30). Examples of delivery aids may include one or
more dispersants or surfactants. In some examples, a surfactant may
help improve the stability and dispersion of the colloidal
suspension. In some examples, system 10 may further include one or
more mixers in order to maintain suspension 26, e.g., maintain
coating material 28 suspended in carrier 20.
[0073] Plasma spray device 20 may include a plasma spray gun
including a cathode and an anode separated by a plasma gas channel.
As the plasma gas flows through the plasma gas channel, a voltage
may be applied between the cathode and anode to cause the plasma
gas to form a plasma. In some such examples, suspension 26 may be
injected inside plasma spray device 20 such that the suspension
flows through part of the plasma gas channel. In other examples,
suspension 26 may be introduced to a plume of the plasma external
to plasma spray device 20. Upon introduction to the plasma gas,
carrier 30 in suspension 26 may evaporate allowing coating material
28 to be heat softened or vaporized followed by the subsequent
deposition of coating material 28 on substrate 16 in the form of a
layer of multi-layer TBC 18.
[0074] System 10 also includes computing device 24. Computing
device 24 may include, for example, a desktop computer, a laptop
computer, a workstation, a server, a mainframe, a cloud computing
system, or the like. Computing device 24 may include or may be one
or more processors, such as one or more digital signal processors
(DSPs), general purpose microprocessors, application specific
integrated circuits (ASICs), field programmable logic arrays
(FPGAs), or other equivalent integrated or discrete logic
circuitry. Accordingly, the term "processor," as used herein may
refer to any of the foregoing structure or any other structure
suitable for implementation of the techniques described herein. In
addition, in some examples, the functionality of computing device
24 may be provided within dedicated hardware and/or software
modules.
[0075] Computing device 24 may be configured to control operation
of system 10, including, for example, stage 14, suspension source
22, and/or plasma spray device 20. For example, computing device 24
may be configured to control operation of stage 14, suspension
source 22, and/or plasma spray device 20 to position substrate 16
relative to suspension source 22 and/or plasma spray device 20. In
such examples, computing device 24 may control suspension source 22
and plasma spray device 20 to maneuver the position of substrate 16
relative to plasma spray device 20 to facilitate the deposition of
multi-layer TBC 18.
[0076] Computing device 24 may be communicatively coupled to at
least one of stage 14, suspension source 22, and plasma spray
device 20 using respective communication connections. Such
connections may be wireless or wired connections.
[0077] In some examples, article 40 may also include one or more
intermediate layers (e.g., a bond coat) positioned between TBC 18
and substrate 16. For example, FIG. 2 is a cross-sectional diagram
of an example article 60 that includes a multi-layer TBC 18
deposited on a bond coat 52 and a substrate 16 using the suspension
plasma spray techniques described herein. Multi-layer TBC 18 may be
the same or substantially the same as multi-layer TBC 18 described
with respect to FIG. 1B apart from any difference noted below.
[0078] Bond coat 52 may be deposited on or deposited directly on
substrate 16 to promote adhesion between substrate 16 and one or
more additional layers deposited on bond coat 52, including, for
example, multi-layer TBC 18 (e.g., first layer 42). In examples in
which substrate 16 includes a superalloy, bond coat 52 may include
an alloy, such as a MCrAlY alloy (where M is Ni, Co, or NiCo), a
.beta.-NiAl nickel aluminide alloy (either unmodified or modified
by Pt, Cr, Hf, Zr, Y, Si, and combinations thereof), a
.gamma.-Ni+.gamma.'-Ni.sub.3Al nickel aluminide alloy (either
unmodified or modified by Pt, Cr, Hf, Zr, Y, Si, and combinations
thereof), or the like. In some examples, bond coat 52 may include
Pt.
[0079] In other examples, bond coat 52 may include ceramics or
other materials that are compatible with substrate 16 that includes
a ceramic or a CMC. For example, bond coat 52 may include mullite
(aluminum silicate, Al.sub.6Si.sub.2O.sub.13), silica, silicides,
silicon, or the like. Bond coat 52 may further include other
ceramics, such as rare earth silicates including lutetium (Lu)
silicates, ytterbium (Yb) silicates, thulium (Tm) silicates, erbium
(Er) silicates, holmium (Ho) silicates, dysprosium (Dy) silicates,
gadolinium (Gd) silicates, terbium (Tb) silicates, europium (Eu)
silicates, samarium (Sm) silicates, promethium (Pm) silicates,
neodymium (Nd) silicates, praseodymium (Pr) silicates, cerium (Ce)
silicates, lanthanum (La) silicates, yttrium (Y) silicates,
scandium (Sc) silicates, or the like.
[0080] Bond coat 52 may be selected based on a number of
considerations, including the chemical composition and phase
constitution of multi-layer TBC 18 (e.g., first layer 42) and
substrate 16. For example, when substrate 16 includes a superalloy
with a .gamma.-Ni+.gamma.'-Ni.sub.3Al phase constitution, bond coat
52 may include a .gamma.-Ni+.gamma.'-Ni.sub.3Al phase constitution
to better match the coefficient of thermal expansion of substrate
16, and therefore increase the mechanical stability (adhesion) of
bond coat 52 to substrate 16. Alternatively, when substrate 16
includes a CMC, bond coat 52 may include silicon and/or a ceramic,
such as, for example, mullite or a rare earth silicate.
[0081] In some examples, bond coat 52 may include multiple layers.
In some such examples, the different layers of bond coat 52 may
perform separate functions. For example, in some examples in which
substrate 16 is a CMC including silicon carbide, bond coat 52 may
include a first layer of silicon deposited on substrate 16,
followed by a second layer including mullite or a rare earth
silicate. The silicon layer may provide better bonding to substrate
16, while the ceramic layer may prevent water vapor from reaching
the silicon layer and/or provide better coefficient of thermal
expansion mating with the layers of TBC 18.
[0082] In some examples, bond coat 52 may be deposited using a
suspension plasma spray technique, e.g., as described herein. In
other examples, bond coat 52 may be deposited using other
techniques including, for example, traditional thermal spraying,
including, air plasma spraying, HVOF spraying, low vapor plasma
spraying; PVD, including EB-PVD, DVD, and cathodic arc deposition;
CVD; slurry process deposition; sol-gel process deposition;
electrophoretic deposition; or the like.
[0083] Bond coat 52 may define any thickness adequate to promote
adherence of an additional layer to substrate 16. For example, bond
coat 52 may have a thickness of less than about 0.008 inches (e.g.,
less than about 200 .mu.m).
[0084] FIG. 2 shows an example article 50 that includes substrate
16, and multi-layer TBC 18 deposited on bond coat 52. In some
examples, article 50 may or may not include all of the layers shown
in FIG. 2, or article 50 may have one or more additional layers
included, such as, for example, an EBC layer, an abradable coating,
an outer CMAS-resistant layer, or the like.
[0085] In some examples, the third layer 46 of TBC 18 may be
separated into two different layers in order to further tailor the
properties of third layer 46. For example, FIG. 3 is a
cross-sectional diagram of another example article 80 that includes
a multi-layer TBC 62 deposited on substrate 16 using a suspension
thermal spray technique as described herein. Multi-layer TBC 62
includes first layer 42, second layer 44, third layer 64, and
fourth layer 66. First layer 42 and second layer 44 may be the same
as first layer 42 and second layer 44 described above with respect
to FIG. 1B, the details of which will not be repeated here.
[0086] The composition of third layer 64 may be the same or
substantially the same as third layer 46 from FIG. 1B that does not
include added alumina. For example, third layer 64 may include
predominately (e.g., the main component or a majority) the third
based oxide (e.g., zirconia) mixed with a minority amounts of the
second rare earth oxide (e.g., ytterbia), the third rare earth
oxide (e.g., samaria), and the fifth rare earth oxide (e.g.,
gadolinia) deposited on second layer 44 as a dense microstructure.
In some examples, third layer 64 may include a tetragonal prime
phase constitution with about 2.5 mol. % ytterbia, about 1 mol. %
gadolina, about 0.5 mol. % samaria, and the balance zirconia and
any impurities present.
[0087] Third layer 64 may include a dense microstructure formed
using the suspension plasma spray techniques described herein. The
increased density of third layer 64 may help prevent exposure of
substrate 16 to deleterious environmental species, prevent
deterioration of multi-layer TBC 62, and increase the service life
of substrate 16.
[0088] In some examples, third layer 64 may have a thickness of
between about 0.0005 inches to about 0.005 inches (e.g., between
about 10 .mu.m to about 130 .mu.m).
[0089] TBC 62 also includes fourth layer 66 on third layer 64. The
composition of fourth layer 66 may be the same or substantially the
same as third layer 46 from FIG. 1B that includes a phase
constitution of alumina. For example, fourth layer 66 may include a
fourth based oxide of zirconia or hafnia, the second rare earth
oxide including ytterbia, the third rare earth oxide including
samaria, and a sixth rare earth oxide including at least one of
lutetia, scandia, ceria, neodymia, europia, and gadolinia (e.g.,
gadolinia) collectively forming a first phase and alumina forming a
second phase. In some examples, the first phase of fourth layer 46
may include a tetragonal prime phase constitution with ytterbia in
a concentration between about 2 mol. % and about 4 mol. % (e.g.,
about 2.5 mol. %), gadolinia in a concentration between about 0.1
mol. % and about 2 mol. % (e.g., about 1 mol. %), samaria in a
concentration between about 0.1 mol. % and about 1 mol. % (e.g.,
about 0.5 mol. %), and the balance zirconia, and the second phase
constitution of alumina. Fourth layer 66 may include between about
10 mol. % and about 50 mol. % of alumina based on the total layer.
As described above, the presence of alumina may help increase the
durability of fourth layer 66 and help protect multi-layer TBC 62
from erosion due to deleterious species, such as, for example,
carbon and sand.
[0090] In some examples, fourth layer 66 may include a dense
microstructure. The increased density of fourth layer 66 may help
prevent exposure of substrate 16 to deleterious environmental
species, prevent deterioration and erosion of multi-layer TBC 62,
and increase the service life of substrate 16. In other examples,
fourth layer 66 may include a columnar microstructure.
[0091] In some examples, fourth layer 66 may have a thickness
between about 0.0005 inches and about 0.003 inches (e.g., between
about 10 .mu.m and about 80 .mu.m).
[0092] Fourth layer 66 may be deposited using the suspension plasma
spray techniques described herein. In other examples, fourth layer
66 may be deposited using other techniques including, for example,
traditional thermal spraying, including, air plasma spraying, HVOF
spraying, low vapor plasma spraying; PVD, including EB-PVD, DVD,
and cathodic arc deposition; CVD; slurry process deposition;
sol-gel process deposition; electrophoretic deposition; or the like
to deposit fourth layer 66 including a dense microstructure or a
columnar microstructure.
[0093] FIG. 4 is a flow diagram illustrating an example technique
70 for depositing a layer on a substrate using suspension plasma
spraying. The technique of FIG. 4 is described with respect to
system 10 of FIG. 1A and second and third layers 44, 46 of article
40 of FIG. 1B for ease of description only. However, the suspension
plasma spray techniques may be used to form other layers/articles
of article 40 and the layers of TBC 18 of FIG. 1B may be formed
using suspension plasma spray techniques other than those described
in FIG. 4 or using other systems than those shown in FIG. 1A.
[0094] Technique 70 of FIG. 4 includes forming suspension 26
including coating material 28 and carrier 30 (72). Coating material
28 and carrier 30 may be substantially the same as those described
above with respect to system 10 of FIG. 1A and article 40 of FIG.
1B. For example, with respect to forming second and third layers
44, 46, coating material 28 may include a respective base oxide
(e.g., zirconia), the second rare earth oxide (e.g., ytterbia), the
third rare earth oxide (e.g., samaria), and an additional rare
earth oxide including at least one of lutetia, scandia, ceria,
neodymia, europia, and gadoliniazirconia, ytterbia, gadolinia
(e.g., gadolinia) mixed with a carrier 30. As described above, the
respective amounts of each oxide may be tailored to formulate a
cubic phase constitution (e.g., second layer 44), a tetragonal
prime phase constitution (e.g., third layer 46), or a combination
thereof depending on the desired properties of the layer. The
particles may be pre-alloyed (e.g., particles of cubic or
tetragonal prime phase constitutions of zirconia, ytterbia,
gadolinia, and samaria) or provided as discrete particles of the
different oxides mechanically mixed in suspension 26 in the desired
compositional amounts.
[0095] In some examples, coating material 28 may have a fine
particle size to facilitate melt softening or vaporization of
coating material 28 by a heated plume (e.g., plasma) of plasma
spray device 20. The average particle size of coating material 28
may be less than about 25 .mu.m or less than about 10 .mu.m, and in
some cases, less than about 1 .mu.m, depending on the desired
microstructure of the resultant layer.
[0096] Altering the size of the particles of coating material 28,
the spraying distance, power of plasma spray device 20, injection
position, size of injection nozzle, surface speed, advance rate,
target temperature, suspension feed rate, carrier 30 or
combinations thereof may affect the microstructure, thickness,
phase(s), and porosity of a deposited layer. For example, where a
columnar microstructure is desired (e.g., second layer 44) the
average particle diameter may be less than about 1 .mu.m such as
between about 0.01 .mu.m and about 1 .mu.m, between about 0.01
.mu.m and about 0.5 .mu.m, or between about 0.01 .mu.m and about
0.05 .mu.m. The very fine particles of coating material 28 may be
deposited using the suspension plasma spray techniques described
herein to form a layer with a columnar microstructure. For example,
as one non-limiting example, the very fine particles may be applied
using a relatively high spraying distance, a relatively high
suspension feed rate, a relatively low power, or combinations
thereof to obtain the columnar microstructure; however other
parameters may also be used to obtain the columnar
microstructure.
[0097] In other examples where a dense microstructure is preferred
(e.g., third layer 46), the fine particles making up coating
material 28 may have an average particle diameter between about 1
.mu.m and about 25 .mu.m, between about 1 .mu.m and about 20 .mu.m,
between about 1 .mu.m and about 10 .mu.m, or between about 1 .mu.m
and about 5 .mu.m. As one non-limiting example, the very fine
particles may be applied using a relatively low spraying distance,
a relatively low suspension feed rate, a relatively high power, or
combinations thereof to obtain the dense microstructure; however
other parameters may also be used to obtain the dense
microstructure. Additionally, because the particles remain
relatively small compared to the particle sizes utilized in other
plasma spray techniques (e.g., >30 .mu.m), the relatively small
particle sizes of coating material 28 may result in the layer
having a reduced pore size compared to a layer deposited using a
traditional thermal spray technique, as the small particles will
pack closer together.
[0098] Coating material 28 may be added to carrier 30 to form
suspension 26. In some examples, suspension 26 may include may
include about 1 to about 30 vol. % solid loading of coating
material 28 in carrier 30. Suspension 26 may further include
delivery aids such as a dispersant or a surfactant. The dispersant
or surfactant may prevent coating material 28 from agglomerating in
carrier 30 and maintain the suspension of coating material 28 in
carrier 30.
[0099] Once suspension 26 is formed, suspension 26 may be
introduced into a heated plume formed by plasma spray device 20
(74). For example, computing device 24 may control suspension
source 22 to provide a controlled amount or rate of suspension 26
into the heated plume formed by plasma spray device 20.
[0100] Suspension 26 may be stored or supplied to plasma spray
device 20 using suspension source 22. Computing device 24 may
control suspension source 22 to introduce a controlled amount of
suspension 26 into the heated plume formed by plasma spray device
20.
[0101] The temperature of the heated plume may, in some examples,
be above about 6000 K, which may result in evaporation of
substantially all (e.g., all or nearly all) of carrier 30. The
evaporation of carrier 30 may leave substantially only coating
material 28 in the heated plume. The high temperature of the heated
plume may also result in melt softening or vaporization of coating
material 28.
[0102] Technique 70 further includes directing coating material 28
toward substrate 16 using the heated plume (76). For example,
computing device 24 may control a position of plasma spray device
20, stage 14, or both, to cause the heated plume to be directed at
a selected location of substrate 16 to result in coating material
28 being deposited at the selected location. The heated plume may
carry coating material 28 toward substrate 16, where coating
material 28 deposits in a layer (e.g., second layer 44 or third
layer 46) on substrate 16 (78).
[0103] In some examples, system 10 may include an inert gas source
(not shown in FIG. 1A), and the inert gas source may supply an
inert gas shroud to coating material 28 in the heated plume during
deposition of coating material 28 on substrate 16. The inert gas
may surround the heated plume as the heated plume exits plasma
spray device 20. The inert gas shroud may reduce in-air oxidation
of coating material 28. In-air oxidation may cause the resulting
multi-layer TBC 18 to have reduced density, cohesive strength, bond
strength, or the like. The inert gas used for the inert gas shroud
may include Ar, N.sub.2, or the like.
[0104] In some examples, while directing coating material 28 toward
substrate 16 using the heated plume (76), computing device 24 may
control plasma spray device 20, stage 14, or both to move plasma
spray device 20 and substrate 16 relative to each other. For
example, computing device 24 may be configured to control plasma
spray device 20 to scan the heated plume relative to substrate 16.
This may cause the cylinder-shaped heated plume that includes
coating material 28 to move relative to substrate 16, and may form
a layer of multi-layer TBC 18 over the surfaces of substrate 16
scanned with the heated plume.
[0105] FIG. 5 is a flow diagram illustrating an example technique
80 for depositing a multi-layer TBC on a substrate using a
suspension plasma spray technique as described herein. The
technique of FIG. 5 is described with respect to articles 40, 50,
and 60 of FIGS. 1B-3 for ease of description only. A person having
ordinary skill in the art will recognize and appreciate that the
technique of FIG. 5 may be used to form articles other than those
of FIGS. 1B-3, and the articles of FIGS. 1B-3 may be formed using
other suspension plasma spray techniques than those described in
FIG. 5.
[0106] Technique 80 includes depositing an optional bond coat 52 on
substrate 16 (82), depositing first layer 42 on substrate 16 (84),
depositing second layer 44 on first layer 42 using plasma spray
device 20 (86), and depositing third layer 46 on second layer 44
using plasma spray device 20 (88).
[0107] The composition of bond coat 52 may be tailored depending on
the composition of underlying substrate 16 in order to improve
adhesion between multi-layer TBC 18 and substrate 16 and may be
substantially the same as described above with respect to FIG. 2.
For example, where substrate 16 includes a super alloy material,
bond coat 52 may include an alloy, such as a MCrAlY alloy or may
include Pt. In other examples where substrate 16 includes a ceramic
or CMC, bond coat 52 may include ceramics.
[0108] In some examples, bond coat 52 may be deposited on substrate
16 using a suspension plasma spray technique, e.g., technique 70 of
FIG. 4. In other examples, the bond coat may be applied using other
techniques including, for example, traditional thermal spraying,
including, air plasma spraying, HVOF spraying, low vapor plasma
spraying; PVD, including EB-PVD, DVD, and cathodic arc deposition;
CVD; slurry process deposition; sol-gel process deposition;
electrophoretic deposition; or the like.
[0109] Technique 80 includes also depositing first layer 42 of
multi-layer TBC 18 on substrate 16 (84). First layer 42 may be
substantially the same as first layer 42 described above with
respect to article 40 of FIG. 1. For example, first layer 42 may
include zirconia and yttria deposited in a columnar microstructure
to provide multi-layer TBC 18 with enhanced thermal cycling
resistance and bonding to underlying substrate 16.
[0110] First layer 42 may be deposited using a first plurality of
particles using the suspension plasma spray techniques of the
present disclosure, e.g., technique 70 of FIG. 1. The first
plurality of particles may include a single particle type, e.g., a
pre-alloyed zirconia and yttria particles, or may include discrete
particles of zirconia and yttria. In some examples, the first
plurality of particles may have an average diameter less than about
1 .mu.m and may be deposited in a predominately columnar
microstructure.
[0111] Technique 80 further includes depositing second layer 44 in
a columnar microstructure on first layer 42 (86). Second layer 44
may be substantially the same as second layer 44 described with
respect to FIG. 1B. For example, second layer 44 may include
zirconia, ytterbia, gadolinia, and samaria deposited in a columnar
microstructure to provide multi-layer TBC 18 with a low thermal
conductivity.
[0112] Second layer 44 may be deposited using a second plurality of
particles using the suspension plasma spray techniques described
herein, e.g., technique 70 of FIG. 4. In some examples, the second
plurality of particles may include a single particle type, e.g., a
pre-alloyed zirconia, ytterbia, gadolinia, and samaria particles.
The pre-alloyed particles may include or substantially include
pre-alloyed particles in a desired phase constitution. For example,
the second plurality of particles may include zirconia, ytterbia,
gadolinia, and samaria including or substantially including a cubic
phase constitution. In other examples, the second plurality of
particles may include discrete particles, e.g., distinct particles
of each of zirconia, ytterbia, gadolinia, and samaria combined to
make up the composition of second layer 44 with the desired phase
constitution. In some examples, depositing second layer 44 as a
cubic phase constitution may provide second layer 44 with a lower
thermal conductivity than a layer having a similar composition with
a tetragonal prime or a compound phase constitution.
[0113] In some examples, the second plurality of particles may
define an average particle size less than about 1 .mu.m which may
aid in depositing second layer 44 as a columnar microstructure. The
columnar microstructure of second layer 44 may provide improved
thermal cycling performance in comparison to layers that do not
possess a columnar microstructure.
[0114] Technique 80 also includes depositing third layer 46, in a
dense microstructure on second layer 44 (88). Third layer 46 may be
substantially the same as third layer 46 described with respect to
FIG. 1B. For example, third layer 46 may include zirconia,
ytterbia, gadolinia, samaria, and optionally, alumina, in a dense
microstructure to help prevent exposure of substrate 16 to
deleterious environmental species, prevent deterioration and
erosion of multi-layer TBC 18, and increase the durability and
service life of substrate 16.
[0115] Third layer 46 may be deposited using a third plurality of
particles using the suspension plasma spray techniques described
herein, e.g., technique 70 of FIG. 4. In some examples, the third
plurality of particles may include a single particle type, e.g., a
pre-alloyed zirconia, ytterbia, gadolinia, and samaria particles.
The pre-alloyed particles may include or substantially include
pre-alloyed particles in a desired phase constitution. For example,
the third plurality of particles may include zirconia, ytterbia,
gadolinia, and samaria including or substantially including a
tetragonal prime phase constitution. In other examples, the third
plurality of particles may include discrete particles, e.g.,
distinct particles of each of zirconia, ytterbia, gadolinia, and
samaria combined to make up the composition of third layer 46 with
the desired phase constitution. In some examples, depositing third
layer 46 as a tetragonal prime phase constitution may provide third
layer 46 with improved thermal cycling resistance than a layer
having a similar composition with a cubic or a compound phase
constitution.
[0116] In some examples, the third plurality of particles may
define an average particle size between about 1 .mu.m and about 25
.mu.m which may aid in depositing third layer 46 with a dense
microstructure. The dense microstructure of third layer 46 may
provide a decreased overall porosity and resultant higher density
in comparison to layers that do not possess a dense
microstructure.
[0117] Technique 80 also includes optionally depositing one or more
additional layers on multi-layer TBC 18 (90). In some examples, the
additional layer be the same or substantially the same as fourth
layer 66 of FIG. 3. For example, fourth layer 66 may include a
first phase constitution of the fourth base oxide (e.g., zirconia),
the second rare earth oxide (e.g., ytterbia), the third rare earth
oxide (e.g., samaria), and the sixth rare earth oxide (e.g.,
gadolinia) collectively, for example, in a tetragonal prime phase
constitution and a second phase of alumina as described with
respect to FIG. 3, where the alumina phase makes up about 10% to
about 50% of the layer. In some examples, fourth layer 66 may be
deposited over a third layer 64 that does not include alumina. The
presence of alumina in fourth layer 66 may increase the overall
durability of article 60 compared to an outer layer on article 60
that does not include alumina.
[0118] Fourth layer 66 may be deposited using a fourth plurality of
particles (e.g., particles of alumina mixed with particles of the
first phase constitution of zirconia, ytterbia, gadolinia, samaria)
and a suspension plasma spray technique, e.g., technique 70 from
FIG. 4. In other examples, fourth layer 66 may be applied using
other techniques including, for example, traditional thermal
spraying, including, air plasma spraying, HVOF spraying, low vapor
plasma spraying; PVD, including EB-PVD, DVD, and cathodic arc
deposition; CVD; slurry process deposition; sol-gel process
deposition; electrophoretic deposition; or the like.
[0119] In some examples, fourth layer 66 may be deposited as a
dense microstructure, a columnar microstructure, or a porous
microstructure to provide desired properties. For example, fourth
layer 66 may be deposited in a columnar microstructure to provide
enhanced thermal cycling resistance, or fourth layer 66 may be
deposited in a dense microstructure to provide enhanced erosion
resistance and durability.
[0120] In some examples, one or more additional layers may be
deposited on third layer 46 or fourth layer 66 including, for
example, other protective or functional layers, such as, for
example, an EBC layer, an abradable coating, a CMAS-resistant
layer, or the like.
[0121] Various examples have been described. These and other
examples are within the scope of the following claims.
* * * * *