U.S. patent application number 13/818331 was filed with the patent office on 2014-09-18 for rare earth silicate environmental barrier coatings.
This patent application is currently assigned to ROLLS-ROYCE CORPORATION. The applicant listed for this patent is Kang N. Lee. Invention is credited to Kang N. Lee.
Application Number | 20140261080 13/818331 |
Document ID | / |
Family ID | 44651949 |
Filed Date | 2014-09-18 |
United States Patent
Application |
20140261080 |
Kind Code |
A1 |
Lee; Kang N. |
September 18, 2014 |
RARE EARTH SILICATE ENVIRONMENTAL BARRIER COATINGS
Abstract
A vapor deposition method may include applying a first electron
beam to vaporize a portion of a first target material comprising a
rare earth oxide, where the first electron beam delivers a first
amount of energy. The method also may include applying a second
electron beam to vaporize a portion of a second target material
comprising silica, where the second electron beam delivers a second
amount of energy different from the first amount of energy. In some
examples, the second target material is separate from the first
target material. Additionally, the portion of the first target
material and the portion of the second target material may be
deposited substantially simultaneously over a substrate to form a
layer over the substrate. A system for practicing vapor deposition
methods and articles formed using vapor deposition methods are also
described.
Inventors: |
Lee; Kang N.; (Zionsville,
IN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lee; Kang N. |
Zionsville |
IN |
US |
|
|
Assignee: |
ROLLS-ROYCE CORPORATION
Indianapolis
IN
|
Family ID: |
44651949 |
Appl. No.: |
13/818331 |
Filed: |
August 24, 2011 |
PCT Filed: |
August 24, 2011 |
PCT NO: |
PCT/US11/48914 |
371 Date: |
June 4, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61377674 |
Aug 27, 2010 |
|
|
|
Current U.S.
Class: |
106/286.5 ;
106/286.1; 118/722; 427/596 |
Current CPC
Class: |
C04B 41/52 20130101;
C04B 41/52 20130101; C04B 41/52 20130101; F05D 2300/611 20130101;
C23C 14/30 20130101; C04B 41/5024 20130101; C04B 41/009 20130101;
C04B 41/85 20130101; C04B 41/5024 20130101; C23C 14/08 20130101;
C04B 41/89 20130101; F01D 5/288 20130101; C04B 41/009 20130101;
C04B 41/5024 20130101; C04B 35/565 20130101; C04B 41/4529 20130101;
C04B 41/4529 20130101; C04B 41/4529 20130101; C04B 41/5024
20130101; C04B 41/4582 20130101; C04B 35/806 20130101; C23C 14/548
20130101; F01D 5/147 20130101 |
Class at
Publication: |
106/286.5 ;
427/596; 118/722; 106/286.1 |
International
Class: |
F01D 5/14 20060101
F01D005/14 |
Claims
1. A vapor deposition method comprising: applying a first electron
beam to vaporize a portion of a first target material comprising a
rare earth oxide, wherein the first electron beam delivers a first
amount of energy; applying a second electron beam to vaporize a
portion of a second target material comprising silica, wherein the
second electron beam delivers a second amount of energy different
from the first amount of energy, and wherein the second target
material is separate from the first target material; wherein the
portion of the first target material and the portion of the second
target material are deposited substantially simultaneously over a
substrate to form a layer over the substrate.
2. The vapor deposition method of claim 1, wherein the layer
comprises a substantially nonporous microstructure.
3. The vapor deposition method of claim 1, wherein the layer
comprises a substantially homogeneous composition.
4. The vapor deposition method of claim 1, wherein the first amount
of energy is between approximately 1.1 and approximately 2 times
greater than the second amount of energy.
5. (canceled)
6. The vapor deposition method of claim 1, wherein applying the
first electron beam and applying the second electron beam comprise
applying an electron beam from a single energy source, the single
energy source alternating between applying the first electron beam
and the second electron beam.
7. The vapor deposition method of claim 1, wherein the rare earth
oxide is selected from the group consisting of an oxide of Gd, an
oxide of Yb, and combinations thereof.
8. The vapor deposition method of claim 1, wherein the layer
comprises a first layer, and further comprising: applying a third
electron beam to vaporize a portion of a third target material
comprising a rare earth oxide, wherein the third electron beam
delivers a third amount of energy; applying a fourth electron beam
to vaporize a portion of a fourth target material comprising
silica, wherein the fourth electron beam delivers a fourth amount
of energy different from the third amount of energy, and the fourth
target material is separate from the third target material; wherein
the portion of the third target material and the portion of the
fourth target material are deposited substantially simultaneously
over the substrate to form a second layer over the substrate.
9.-12. (canceled)
13. The vapor deposition method of claim 1, further comprising
applying a third electron beam to vaporize a portion of a third
target material, wherein the third electron beam delivers a third
amount of energy, and wherein the portion of the third target
material is deposited, substantially simultaneously with the
portion of the first target material and the second target
material, over the substrate to form the layer.
14. The vapor deposition method of claim 13, wherein the third
target material comprises alumina.
15. (canceled)
16. The vapor deposition method of claim 1, wherein the layer
comprises at least 50 weight percent rare earth silicate, formed by
combination of at least some of the rare earth oxide and at least
some of the silica.
17. The vapor deposition method of claim 16, wherein the layer
comprises a first layer formed over the substrate and a second
layer formed over the first layer, the first layer comprising the
rare earth disilicate, the second layer comprising the rare earth
monosilicate.
18. (canceled)
19. A system comprising: a vacuum chamber; a first electron beam
source configured to deliver a first electron beam to vaporize a
portion of a first target material comprising a rare earth oxide,
wherein the first electron beam delivers a first amount of energy;
a second electron beam source configured to deliver a second
electron beam to vaporize a portion of a second target material
comprising silica, wherein the second electron beam delivers a
second amount of energy different from the first amount of energy;
and a substrate, wherein the system is configured to substantially
simultaneously deposit the portion of the first target material and
the portion of the second target material in a layer over the
substrate, and wherein the system is configured to deliver the
first amount of energy so the first amount of energy is between
approximately 1.1 and approximately 2 times greater than the second
amount of energy.
20. The system of claim 19, wherein the system is configured to
substantially simultaneously deposit the portion of the first
target material and the portion of the second target material in a
substantially homogeneous layer.
21. The system of claim 19, further comprising a transonic gas
stream source.
22. (canceled)
23. The system of claim 19, wherein the system is configured to
substantially simultaneously deposit the portion of the first
target material and the portion of the second target material in a
substantially nonporous layer.
24. The system of claim 19, wherein the system is configured to
substantially simultaneously deposit the portion of the first
target material and the portion of the second target material in a
columnar layer.
25. (canceled)
26. An article comprising: a substrate; and an environmental
barrier coating formed over the substrate, wherein the
environmental barrier coating comprises a first material having a
first vapor pressure and a second material having a second vapor
pressure different from the first vapor pressure, wherein the first
material is deposited from a first target material that comprises a
rare earth oxide by applying a first electron beam to vaporize a
portion of the first target material, the first electron beam
delivering a first amount of energy, wherein the second material is
deposited from a second target material that comprises silica by
applying a second electron beam to vaporize a portion of the second
target material, the second electron beam delivering a second
amount of energy, wherein the first amount of energy is between
approximately 1.33 and approximately 1.47 times greater than the
second amount of energy.
27. The article of claim 26, wherein the environmental barrier
coating comprises a substantially nonporous microstructure.
28. The article of claim 26, wherein the environmental barrier
coating comprises a columnar microstructure.
29. The article of claim 26, wherein the environmental barrier
coating further comprises alumina, wherein the alumina is deposited
from a third target material that comprises alumina by applying a
third electron beam to vaporize a portion of the third target
material, the third electron beam delivering a third amount of
energy.
30. (canceled)
Description
TECHNICAL FIELD
[0001] This disclosure relates to environmental barrier coatings
and, more particularly, to rare earth silicate environmental
barrier coatings.
BACKGROUND
[0002] Components of high-temperature mechanical systems, such as,
for example, gas-turbine engines, must operate in severe
environments. For example, the high-pressure turbine blades and
vanes exposed to hot gases in commercial aeronautical engines
typically experience metal surface temperatures of about
1000.degree. C., with short-term peaks as high as 1100.degree.
C.
[0003] Some components of high-temperature mechanical systems
include a Ni or Co-based superalloy substrate. In an attempt to
reduce the temperatures experienced by the substrate, the substrate
can be coated with a thermal barrier coating (TBC). The TBC may
include a thermally insulative ceramic topcoat and is bonded to the
substrate by an underlying metallic bond coat. The TBC, usually
applied either by air plasma spraying or electron beam physical
vapor deposition, is most often a layer of yttria-stabilized
zirconia (YSZ) with a thickness of about 100 micrometers (.mu.m) to
about 500 nm. The properties of YSZ include low thermal
conductivity, high oxygen permeability, and a relatively high
coefficient of thermal expansion. The YSZ TBC is also typically
made "strain tolerant" and the thermal conductivity further lowered
by depositing a structure that contains numerous pores and/or
pathways.
[0004] Economic and environmental concerns, i.e., the desire for
improved efficiency and reduced emissions, continue to drive the
development of advanced gas turbine engines with higher inlet
temperatures. Some components of high-temperature mechanical
systems include a ceramic or ceramic matrix composite (CMC)
substrate, which may allow an increased operating temperature
compared to a component with a superalloy substrate. The ceramic or
CMC substrate can be coated with an environmental barrier coating
(EBC) to reduce exposure of a surface of the substrate to
environmental species, such as water vapor or oxygen. In some
embodiments, the EBC also may provide some thermal insulation to
the ceramic or CMC substrate. The EBC may include a ceramic
topcoat, and may be bonded to the substrate by an underlying
metallic or ceramic bond coat.
SUMMARY
[0005] In general, the disclosure is directed to rare earth
silicate environmental barrier coatings and vapor deposition
techniques used to create environmental barrier coatings. In some
embodiments, the vapor deposition techniques include depositing a
rare earth oxide from a first target material and substantially
simultaneously depositing silica from a second target material.
[0006] It has been found that depositing an EBC using vapor
deposition, such as EB-PVD, from at least two sources may mitigate
the difficulty of controlling the composition of an EBC including
at least two components. For example, an EBC including at least two
components may be deposited from at least two material sources. In
some embodiments, the amount of energy provided to each of the
material sources may be controlled independently to result in a
desired composition of the EBC. For example, an electron beam of a
substantially constant power may be directed at each of the
material sources for different relative residence times to control
the relative amount of energy directed at the respective material
sources. As another example, a power level of an electron beam may
be changed when the electron beam is directed at different material
sources. As an additional example, at least two electron beams may
be utilized, each beam being directed to a respective material
target. In some embodiments, the power of at least one of the
electron beams is different than a power of at least one other of
the electron beams.
[0007] In one aspect, the disclosure is directed to a vapor
deposition method that includes applying a first electron beam to
vaporize a portion of a first target material comprising a rare
earth oxide, wherein the first electron beam delivers a first
amount of energy, and applying a second electron beam to vaporize a
portion of a second target material comprising silica, wherein the
second electron beam delivers a second amount of energy different
from the first amount of energy. According to this aspect of the
disclosure, the second target material is separate from the first
target material. Additionally, according to this method, the
portion of the first target material and the portion of the second
target material are deposited substantially simultaneously over a
substrate to form a layer over the substrate.
[0008] In another aspect, the disclosure is directed to a system
including a vacuum chamber and a first electron beam source
configured to deliver a first electron beam to vaporize a portion
of a first target material comprising a rare earth oxide, wherein
the first electron beam delivers a first amount of energy.
According to this aspect of the disclosure, the system also
includes a second electron beam source configured to deliver a
second electron beam to vaporize a portion of a second target
material comprising silica. The second electron beam delivers a
second amount of energy different than the first amount of energy.
The system further includes a substrate. The system is configured
to substantially simultaneously deposit the portion of the first
target material and the portion of the second target material in a
layer over the substrate. In addition, the system is configured to
deliver the first amount of energy so the first amount of energy is
between approximately 1.1 and approximately 2 times greater than
the second amount of energy.
[0009] In another aspect, the disclosure is directed to an article
that includes a substrate and an environmental barrier coating
formed over the substrate. According to this aspect of the
disclosure, the environmental barrier coating includes a first
material having a first vapor pressure and a second material having
a second vapor pressure different from the first vapor pressure.
The first material is deposited from a first target material that
includes a rare earth oxide by applying a first electron beam to
vaporize a portion of the first target material, the first electron
beam delivering a first amount of energy. The second material is
deposited from a second target material that comprises silica by
applying a second electron beam to vaporize a portion of the second
target material, the second electron beam delivering a second
amount of energy. In addition, the first amount of energy is
between approximately 1.33 and approximately 1.47 times greater
than the second amount of energy.
[0010] The details of one or more embodiments of this disclosure
are set forth in the accompanying drawings and the description
below. Other features, objects, and advantages of this disclosure
will be apparent from the description and drawings, and from the
claims.
BRIEF DESCRIPTION OF DRAWINGS
[0011] FIGS. 1A and 1B are cross-sectional schematic diagrams of an
example of a substrate coated with an environmental barrier
coating.
[0012] FIG. 2 is a schematic diagram of an example of a vapor
deposition chamber for coating a substrate from two different
source materials.
[0013] FIG. 3 is a cross-sectional schematic diagram of an example
of a substrate coated with a multi-layered environmental barrier
coating
[0014] FIG. 4 is a cross-sectional schematic diagram of an example
of a substrate coated with a bond coat and an environmental barrier
coating.
[0015] FIG. 5 is a schematic diagram of an example of a vapor
deposition chamber for coating a substrate from three different
source materials.
[0016] FIG. 6 is a cross-sectional schematic diagram of an example
of a substrate coated with an environmental barrier coating and an
overlay coating.
[0017] FIG. 7 is a cross-sectional schematic diagram of an example
of a substrate coated with a bond coat, an environmental barrier
coating, and an overlay coating.
[0018] FIGS. 8A and 8B illustrate a pair of x-ray diffraction
patterns for a powder of environmental barrier coating material and
for an applied environmental barrier coating.
[0019] FIG. 9 is an enlarged image of an example of a dense
microstructure environmental barrier coating created using a
directed vapor deposition technique.
[0020] FIG. 10 is an enlarged image of an example of a columnar
microstructure environmental barrier coating created using a
directed vapor deposition technique.
[0021] FIG. 11 is a cross-sectional image of an example of a
substrate adjacent to an environmental barrier coating created
using a directed vapor deposition technique. The entire structure
was subject to thermal cycling.
[0022] FIG. 12 is a cross-sectional image of an example of a
substrate adjacent to a two layer environmental barrier coating
created using a directed vapor deposition technique. The entire
structure was subject to thermal cycling.
DETAILED DESCRIPTION
[0023] In general, the disclosure relates to rare earth silicate
environmental barrier coatings (EBCs) and vapor deposition
techniques used to create rare earth silicate EBCs. The vapor
deposition techniques may remove a portion of material from at
least one target material and deposit the removed target material
onto a surface of a component to form an EBC. In subsequent use,
the EBC may protect the component from operating conditions that
may otherwise degrade the component.
[0024] Some EBCs have been deposited on a substrate via plasma
spraying. Although plasma spraying may produce an EBC with
acceptable properties for some applications, in other applications,
a plasma spray-deposited EBC may be disadvantageous. For example,
an EBC deposited by plasma spraying may have a surface roughness
which is disadvantageous in applications where low surface
roughness improves aerodynamic performance, such as, for example,
on a gas turbine engine blade. Additionally, an EBC deposited by
plasma spraying may have erosion and/or sinter resistance that is
less than desired for some applications.
[0025] According to one aspect of the disclosure, an EBC may be
deposited on a substrate via a vapor deposition technique, such as,
for example, electron beam physical vapor deposition (EB-PVD) or
directed vapor deposition (DVD). In some embodiments, the EBC may
include more than one component. For example, an EBC may include a
rare earth silicate, which is formed from a rare earth oxide and
silica.
[0026] In some instances, the at least two components may have
different physical or chemical properties which make controlled,
simultaneous deposition difficult. For example, silica and a rare
earth oxide may have different heats of vaporization and/or vapor
pressures at a given temperature and pressure. Accordingly, a rare
earth oxide and silica may have different vaporization rates when
exposed to similar amounts of energy. Thus, when deposition of
silica and a rare earth oxide using EB-PVD from a single material
source is attempted, the resulting coating may have a different
composition than the material source composition.
[0027] However, it has been found that depositing an EBC using
vapor deposition, such as EB-PVD, from at least two sources may
mitigate the difficulty of controlling composition of an EBC
including at least two components. For example, an EBC including at
least two components may be deposited from at least two material
sources. In some embodiments, the amount of energy provided to each
of the material sources may be controlled independently to result
in a desired composition of the EBC. For example, an electron beam
of a substantially constant power may be directed at each of the
material sources for different relative residence times to control
the relative amount of energy directed at the respective material
sources. As another example, a power level of an electron beam may
be changed when the electron beam is directed at different material
sources. As an additional example, at least two electron beams may
be utilized, each beam being directed to a respective material
target. In some embodiments, the power of at least one of the
electron beams is different than a power of at least one other of
the electron beams.
[0028] FIGS. 1A and 1B are cross-sectional schematic diagrams of an
example article 10 that may be used in a high-temperature
mechanical system. Article 10 includes EBC 14 formed over substrate
12. EBC 14 may be a single EBC layer or may include multiple EBC
layers. For example, article 10 in FIG. 1A includes an EBC 14
formed of a single layer, while article 11 in FIG. 1B includes an
EBC 15 formed of a first EBC layer 16 and a second EBC layer 18.
The selection and formation of one or more EBC layers 16, 18 may
depend on a variety of factors, as described in greater detail
below.
[0029] Substrate 12 may be a component configured for use in a high
temperature mechanical system. For example, the high temperature
mechanical system may be a turbine engine and substrate 12 may be a
turbine blade, turbine vane, turbine blade track, turbine
combustion liner, or the like. Because substrate 12 may be
configured for used in a high temperature mechanical system,
substrate 12 may be formed from any material or combination of
materials suitable for use in a high temperature mechanical system.
Materials suitable for use in a high temperature mechanical system
may include a superalloy, a metal-silicon alloy, a ceramic,
including a ceramic matrix composite (CMC), or other similar
materials capable operating at high temperatures. In some
embodiments, substrate 12 may include a Ni- or Co-based
superalloy.
[0030] In some embodiments, substrate 12 may be a metal-silicon
alloy, such as a molybdenum-silicon alloy (e.g., MoSi.sub.2),
niobium-silicon alloy (e.g., NbSi.sub.2), or the like. When
substrate 12 is a metal-silicon alloy, the metal-silicon alloy may
include additional elements to alter the mechanical performance of
the alloy. Elements that affect properties such as toughness,
hardness, temperature stability, corrosion resistance, and
oxidation resistance are known in the art and may be used in
substrate 12.
[0031] As noted, substrate 12 may also be a ceramic. For example, a
suitable ceramic for substrate 12 may be a ceramic that includes
silicon, such as a silicon carbide (SiC), silicon nitride
(Si.sub.3N.sub.4), or similar silicon-containing ceramic.
[0032] In further examples, substrate 12 may include a ceramic
matrix composite (CMC). The CMC may include a matrix material such
as silicon carbide, silicon nitride, alumina, silica, or the like.
The CMC may also include a filler material, and the filler material
may provide continuous reinforcement or a discontinuous
reinforcement. For example, the filler material may include
discontinuous whiskers, platelets, or particulates. As another
example, the filler material may include a continuous monofilament
or multifilament weave.
[0033] The filler composition, shape, size, and the like may be
selected to provide desired properties to the CMC. For example, the
filler material may be chosen to increase the toughness of a
brittle ceramic matrix. Other CMC properties can also be tailored
with the addition of a filler material. For instance, a filler
material may affect thermal conductivity, electrical conductivity,
thermal expansion, hardness, or other desired properties of the
CMC.
[0034] In some embodiments, the filler composition is the same as a
ceramic matrix material. For example, a silicon carbide matrix may
surround silicon carbide whiskers. In other cases, the filler
material may include a different composition than the ceramic
matrix, such as mullite fibers in an alumina matrix. As a
particular example, a CMC may include silicon carbide continuous
fibers embedded in a silicon carbide matrix.
[0035] In accordance with the disclosure, EBC 14 is formed over at
least a portion of substrate 12, as illustrated in FIG. 1A. EBC may
function to protect substrate 12 from environmental attack and, in
some embodiments, thermal effects. As a result, EBC may include
materials that are resistant to environmental degradation, such as
oxidation and water vapor attack. Exemplary EBC materials include
components such as alumina, zirconia, hafnia, rare earth
oxide-stabilized zirconia, rare earth oxide-stabilized hafnia, a
rare earth silicate, a glass ceramic, mullite, and combinations
thereof. In some examples, a glass ceramic may include a barium
strontium alumina silicate
(BaO.sub.x--SrO.sub.1-x--Al.sub.2O.sub.3-2SiO.sub.2), a barium
alumina silicate (BaO--Al.sub.2O.sub.3-2SiO.sub.2), a strontium
alumina silicate (SrO--Al.sub.2O.sub.3-2SiO.sub.2), a calcium
alumina silicate (CaO--Al.sub.2O.sub.3-2SiO.sub.2), a magnesium
alumina silicate (2MgO-2Al.sub.2O.sub.3-5SiO.sub.2), or a lithium
alumina silicate (Li.sub.2O--Al.sub.2O.sub.3-2SiO.sub.2).
[0036] In some embodiments, EBC 14 may include a rare earth
silicate. An EBC including a rare earth silicate may exhibit good
chemical compatibility with an underlying substrate, such as a
substrate that contains silicon. An EBC 14 including a rare earth
silicate may also maintain its structure at high temperatures, thus
enabling use of the component including an EBC 14 comprising a rare
earth silicate at relatively high temperatures. In addition, an EBC
14 including a rare earth silicate may exhibit low volatility
(e.g., low reactivity and volatilization) under high temperature
and high pressure conditions.
[0037] Suitable rare earth silicates for use in EBC 14 may include
a rare earth monosilicate, represented as RE.sub.2SiO.sub.5 or
RE.sub.2O.sub.3--SiO.sub.2, where RE is a rare earth element; a
rare earth disilicate, represented as RE.sub.2Si.sub.2O.sub.7 or
RE.sub.2O.sub.3-2SiO.sub.2, where RE is a rare earth element, or
combinations thereof. In some examples, EBC 14 may include only a
single rare earth silicate, while in other examples, EBC 14 may
include multiple rare earth silicates. EBC 14 may include, for
example, a silicate of at least one of Lanthanum (La), Praseodymium
(Pr), Neodymium (Nd), Promethium (Pm), Samarium (Sm), Europium
(Eu), Gadolinium (Gd), Terbium (Tb), Dysprosium (Dy), Holmium (Ho),
Erbium (Er), Thulium (Tm), Ytterbium (Yb), Lutetium (Lu), Yttrium
(Y), or Scandium (Sc). In addition to a rare earth silicate
material, EBC 14 may include silica (e.g., SiO.sub.2) and/or rare
earth oxide (e.g., RE.sub.2O.sub.3) that includes of one or more
rare earth elements.
[0038] In accordance with one aspect of the disclosure, the rare
earth silicate may be deposited on substrate 12 as a rare earth
oxide and silica. At least some of the rare earth oxide and silica
may then react or combine to form a rare earth disilicate or rare
earth monosilicate. Accordingly, in some embodiments, and EBC 14
which includes a rare earth silicate may include a rare earth
oxide, silica, a rare earth monosilicate, and/or a rare earth
disilicate.
[0039] In some embodiments, EBC 14 may include greater than or
equal to approximately 50 volume percent rare earth silicate, such
as greater than or equal to approximately 75 volume percent rare
earth silicate, or greater than or equal to approximately 90 volume
percent rare earth silicate. For example, EBC 14 may include
greater than or equal to approximately 50 volume percent rare earth
silicate while the remaining portion of EBC 14 may include free
(i.e., unreacted) rare earth oxide and/or free silica.
[0040] As will be described in greater detail below, EBC 14 can be
formed with different microstructures. The different
microstructures of EBC 14 may affect the subsequent performance of
the EBC 14. For example, EBC 14 may be formed with a dense
microstructure that is substantially nonporous. A substantially
nonporous microstructure may prevent environmental species such as
water vapor, oxygen, molten salt, or
calcia-magnesia-alumina-silicate (CMAS) deposits from contacting
substrate 12 and degrading the material structure of substrate 12.
For example, water vapor may react with a substrate 12 including a
CMC and volatilize silica or alumina components in substrate 12.
Consequently, an EBC 14 which is substantially nonporous may
provide protection to substrate 12 by preventing water vapor from
contacting and reacting with substrate 12. In some examples, an EBC
14 with a dense microstructure may have a porosity of less than
about 10 vol. %, such as, e.g., less than about 5 vol. %, where
porosity is measured as a percentage of pore volume divided by
total volume of EBC 14.
[0041] In some embodiments, EBC 14 may alternatively have a
columnar microstructure. A columnar microstructure may have
microcracks or microgaps that extend through at least a portion of
EBC 14 in a direction that is substantially orthogonal to the plane
defined by the EBC coating surface (i.e., in the x-direction
indicated in FIG. 1A). Because of the microgaps, a columnar
microstructure may have enhanced mechanical compliance under
thermal cycling or when a temperature gradient exists, such as when
a high-temperature system is first engaged. Additionally, an EBC 14
having a columnar microstructure may provide improved thermal
protection to substrate 12 compared to an EBC 14 that is
substantially nonporous. While not wishing to be bound by theory,
the microcracks or microgaps may provide scattering sites for
thermal energy-carrying phonons, which may lower an effective
thermal conductivity of an EBC 14 having a columnar microstructure
compared to a substantially nonporous EBC 14 of a similar
composition.
[0042] In some embodiments, thermal protection and mechanical
compliance are not the only benefits of a columnar microstructure
EBC. An EBC 14 having a columnar microstructure may also exhibit
enhanced erosion resistance and enhanced sintering resistance
relative to an EBC 14 which includes a substantially nonporous
microstructure.
[0043] In some examples, as illustrated in FIG. 1B, an article 11
may include an EBC 15 having a first EBC layer 16 and a second EBC
layer 18. In some embodiments, first EBC layer 16 and second EBC
layer 18 may have different microstructures and/or different
compositions, while in other embodiments, first EBC layer 16 and
second EBC layer 18 may have similar microstructures and/or similar
compositions. For example, first EBC layer 16 may include a
columnar microstructure and second EBC layer 18 may include a
substantially dense microstructure. Conversely, first EBC layer 16
may include a substantially dense microstructure and second EBC
layer 18 may include a columnar microstructure.
[0044] With respect to the composition of first and second EBC
layers 16, 18, in some embodiments, the first and second EBC layers
16, 18 may include the same components in similar proportions. In
other embodiments, first and second EBC layers 16, 18 may include
the same components in different proportions. For example, EBC
layer 16 may include a rare earth disilicate while EBC layer 18 may
include a rare earth monosilicate. The interface between EBC layer
16 and EBC layer 18 may be discrete, where there is a sharp
compositional transition between EBC layer 16 and EBC layer 18.
Alternatively, the interface between EBC layer 16 and EBC layer 18
may be compositionally graded, where the interface transitions from
being compositionally similar to EBC layer 16 adjacent EBC layer 16
to being compositionally similar to EBC layer 18 adjacent to EBC
18. In still other embodiments, first and second EBC layers 16, 18
may include the different components (e.g., different rare earth
oxides) in similar or different proportions.
[0045] In some embodiments, the technique according to which EBC 14
or 15 (collectively "EBC 14") is formed may affect performance of
the EBC 14. For example, when a composition of EBC 14 deviates from
an intended chemical composition, environmental and thermal forces
may degrade the EBC 14 more quickly than predicted based on the
intended composition. In some cases, the failure of EBC 14 may lead
to the failure of the component coated with EBC 14 due to damage of
substrate 12.
[0046] EBC 14 may be applied using various techniques. For example,
some techniques include plasma spraying, electron beam physical
vapor deposition (EB-PVD), and chemical vapor deposition (CVD).
Certain techniques may be disadvantageous in certain embodiments.
For example, EB-PVD generally operates by applying an energy source
to a single ingot of target material. The target material vaporizes
and migrates to a substrate, resulting in a deposited EBC 14. In
some examples, the various components that comprise the target
material may have different physical properties, such as different
heats of vaporization or different vapor pressures. As a result,
EBC 14 formed from the single target material may have a different
chemical composition, such as a different ratio of components, than
the target material.
[0047] By contrast, this disclosure provides vapor deposition
systems and techniques that use multiple target materials, such as
at least two target materials, to form EBC 14. Each target material
can include at least one chemical component, and the vaporization
rates of the different target materials can be independently
controlled. As a result, vaporization of the different target
materials can be controlled to create EBC 14 with a desired
chemical composition. For instance, the ratio of energy delivered
to a first target material and a second target material can be
adjusted to achieve EBC 14 with a desired chemical composition.
[0048] FIG. 2 is a schematic diagram of a vapor deposition chamber
24 that may be used to deposit an EBC 14 (FIG. 1A) on a target
substrate 26 using a first target material 30 and a second target
32.
[0049] As illustrated, vapor deposition chamber 24 encloses a
target substrate 26 and an energy source 28. Energy source 28 is
positioned to direct a first energy beam 36 toward a first portion
of a first target material 30 and a second energy beam 38 toward a
first portion of a second target material 32. In some embodiments,
the energy beams 36, 38, may include electron beams. Energy source
28 can scan between first target material 30 and second target
material 32 to deliver energy to first target material 30 and
second target material 32 at different rates and/or for different
amounts of time. In some embodiments, deposition chamber 24
operates at vacuum conditions that are generated through vacuum
port 34. Further, target substrate 26 may be coupled to a stage 25
which rotates and/or translates in one or more directions during
the vapor deposition process to facilitate uniform coating of the
substrate 26.
[0050] First target material 30 and second target material 32 may
include any elements and/or compounds that are deposited on target
substrate 26 to form an EBC 14. In some examples, first target
material 30 includes at least one rare earth oxide (e.g.,
RE.sub.2O.sub.3, where RE is a rare earth element) while second
target material 32 includes silica. Suitable rare earth elements
that may form part of a rare earth oxide composition may include
La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, or Sc.
In some embodiments, a vaporized portion of first target material
30 may react during or after deposition on target substrate 26 with
a vaporized portion of second target material 32 to form an EBC
composition. For example, vaporized rare earth oxide may react with
vaporized silica to form a rare earth monosilicate and/or a rare
earth disilicate.
[0051] Additional or different target materials optionally may be
used in vapor deposition chamber 24, as will be described below. In
some examples, one or more additional target materials may be used
with first target material 30 and second target material 32 to
change the properties of an EBC 14 formed from first target
material 30 and second target material 32. Additional target
materials may include Al.sub.2O.sub.3, TiO.sub.2, Ta.sub.2O.sub.5,
HfSiO.sub.4, ZiSiO.sub.4, an alkali metal oxide, an alkali earth
metal, or combinations thereof.
[0052] Alternatively or additionally, vapor deposition chamber 24
may be used to deposit different types of layers other than an EBC
14. For example, vapor deposition chamber 24 may be used to form a
layer that resists chemical attack by
calcia-magnesia-alumina-silicate deposits. Accordingly, first
target material 30 may include a rare earth oxide while second
target material 32 may include alumina. In some examples,
additional target materials may used to form a layer that resists
calcia-magnesia-alumina-silicate deposits. For example, an
additional target material may include silica. Alternatively,
multiple additional target materials may include a target material
of silica and at least one target material selected from the group
of Ta.sub.2O.sub.5, HfSiO.sub.4, TiO.sub.2, alkali oxides, and
alkali earth oxides.
[0053] Regardless of the specific number or composition of target
materials 30, 32, a target material 30, 32 can have any suitable
size and shape. The size and shape of a target material 30, 32 may
vary based, for example, on the configuration of vapor deposition
chamber 24 and the size or shape of substrate 26 to be coated. In
some examples, a target material 30, 32 may take the shape of an
ingot.
[0054] Vapor deposition chamber 24 may be configured for different
deposition techniques. For example, vapor deposition chamber 24 may
be configured for EB-PVD. In general, EB-PVD uses high-energy beams
36, 38 including electrons that are generated from one or more
electron guns. Accordingly, energy source 28 may be an electron
gun. As described above, the energy beam may conceptually be
referred to as a first energy beam 36, which is directed onto first
target material 30 and a second energy beam 38, which is directed
onto second target material 32. In some embodiments, energy source
28 is controlled to variably direct the energy beam onto first
target material 30 and second target material 32 to melt and
evaporate portions of target materials 30, 32. In this manner,
first energy beam 36 and second energy beam 38 may, in fact, be a
single energy beam which is scanned such that the beam 36, 38 is
alternately directed to first target material 30 and second target
material 32. In other examples, first energy beam 36 and second
energy beam 38 may be discrete energy beams and may be generated at
different times by a single energy source 28, as illustrated in
FIG. 2, or may be generated by two separate energy sources.
[0055] In the example of FIG. 2, vapor deposition chamber 24
includes vacuum port 34. A vacuum may be drawn through vacuum port
34 using, for example, a vacuum pump or gas injectors system. The
number, type, or positioning of vacuum port 34 is not critical. In
some examples, vacuum port 34 facilitates gas flow in vapor
deposition chamber 24 to promote migration of vaporized target
material to substrate 26. In some examples, vapor deposition
chamber 24 may operate between atmospheric pressure and a pressure
of approximately 1.times.10.sup.-8 Pascals (1.times.10.sup.-10
millibar). In other examples, such as when vapor deposition chamber
24 is configured for EB-PVD, vapor deposition chamber 24 may
operate at a vacuum between approximately 1.times.10.sup.-6 Pascals
(1.times.10.sup.-8 millibar) and approximately 0.01 Pascals (0.0001
millibar). In additional or alternative examples, such as when
vapor deposition chamber 24 is configured for DVD, vapor deposition
chamber 24 may operate at a vacuum between approximately 0.1
Pascals (0.001 millibar) and approximately 100 Pascals (1
millibar).
[0056] In some embodiments, a pressure gradient is created across
deposition chamber 24 via vacuum port 34, thereby allowing
vaporized portions of first target material 30 and second target
material 32 to migrate to a surface of target substrate 26. Upon
reaching target substrate 26, the vaporized portions of target
materials 30, 32 may deposit on the surface of target substrate 26.
In some embodiments, at least some of the portions of target
materials 30, 32 may react to form a different composition (e.g., a
different composition than that of individual target materials 30
and 32). For example, when first target material 30 includes a rare
earth oxide and second target material 32 includes silica, at least
some of the rare earth oxide and silica may react to form a rare
earth monosilicate and/or a rare earth disilicate. In some cases,
target substrate 26 is rotated and/or translated in vapor
deposition chamber 24 to promote the formation of an EBC 14 of
substantially uniform thickness on target substrate 26.
[0057] In some embodiments, vapor deposition chamber 24 may
alternatively be configured for directed vapor deposition (DVD).
DVD may be similar to EB-PVD in that an energy source 28 which
generates an electron beam operates in a deposition chamber 24 with
a pressure gradient. Additionally, the DVD process may also include
one or more gas streams that direct the clouds of vaporized target
materials 30, 32 onto target substrate 26. For instance, a gas
stream may operate at transonic conditions and may include, but is
not limited to, oxygen, nitrogen, helium, and combinations thereof.
In this manner, a DVD process may provide more coating control than
an EB-PVD process. Additional control of vaporized target materials
30, 32 may improve coating formation and/or coating uniformity on
target substrate 26. For example, a DVD process may improve coating
uniformity on surfaces of substrate 26 that are not readily exposed
to a cloud of vaporized target material 30, 32 without direction of
the cloud of vaporized target material 30, 32, such as surfaces
that are not in a line-of-sight between first target material 30
and substrate 26 and/or second target material 32 and substrate
26.
[0058] In other embodiments, vapor deposition chamber 24 may take
other configurations. For example, energy source 28 may not be an
electron beam source but instead may be a different type of energy
source. Any type of energy source 28 that can vaporize a portion of
a target material 30, 32 for subsequent deposition on target
substrate 26 can be employed. For example, energy source 28 may be
a laser and vapor deposition chamber 24 may be configured for laser
deposition techniques.
[0059] As seen in FIG. 2, a single energy source 28 may direct an
energy beam entirely at first target material 30, entirely at
second target material 32, or variably at first target material 30
and second target material 32.
[0060] In alternate examples, vapor deposition chamber 24 may
include multiple energy sources. For example, a first energy source
may used to vaporize a portion of first target material 30 and a
second energy source may be used to vaporize a portion of second
target material 32. This concept may be extended to any number of
energy sources and target materials. In some embodiments, a number
of energy sources and a number of target materials may not be
equal, and an energy source may be utilized to deliver energy to
more than one target material. Any suitable number of energy
sources may be included in vapor deposition chamber 24.
[0061] Regardless of the specific number of energy sources included
in vapor deposition chamber 24, each energy source 28 can direct an
energy beam 36, 38 (collectively, "energy beam 36"), such as an
electron beam, at a target material 30, 32. Energy beam 36 may
include a continuous waveform, a pulsed waveform, or a weaved
waveform which includes continuous and/or pulsed segments. Further,
energy beam 36 may be directed at a single spot on a target
material 30, 32 or beam 36 may be translated across a surface of
target material 30, 32 to achieve vaporization of portions of the
target material 30, 32 at different locations along the surface of
the target material 30, 32. In some examples, energy beam 36 may be
translated across a surface of target material 30, 32 to provide
substantially uniform heating of the target material 30, 32, such
that vaporization of the material 30, 32, is substantially uniform
across the surface of material 30, 32. In some examples, energy
beam 36 may be focused to a beam spot size less than approximately
1.0 mm, such as less than approximately 0.5 mm, or less than
approximately 0.35 mm.
[0062] When a single energy source 28 directs an energy beam 36 to
multiple target materials 30, 32, such as energy source 28 in FIG.
2, the energy source 28 may alternately direct different energy
beams 36, 38 to the different target materials 30, 32. The rate at
which energy source 28 switches direction of energy beam 36 between
different target materials 30, 32 may be referred to as a scanning
frequency. In some examples where energy source 28 directs a first
energy beam 36 to first target material 30, which includes a rare
earth oxide, and directs a second energy beam 38 to second target
material 32, which includes silica, a scanning frequency of energy
source 28 may be between approximately 3 and approximately 20
hertz, such as between approximately 5 and approximately 15
hertz.
[0063] In some embodiments, energy source 28 may direct first
energy beam 36 at first target material 30 and second energy beam
38 at second target material 32 in a manner which leads to
deposition of portions of first target material 30 and second
target material 32 on target substrate 26 in a single layer. In
such embodiments, vaporized portions of the first target material
30 and vaporized portions of the second target material 32 may be
considered to be substantially simultaneously deposited on target
substrate 26. In some embodiments, this may indicate that portions
of first target material 30 and portions of second target material
32 mix when deposited to form a layer on target substrate 26, e.g.,
portions of first target material 30 and second target material 32
form a single layer instead of a plurality of sub-layers of
material from first target material 30 and second target material
32, respectively. In some embodiments, the layer deposited from
first target material 30 and second target material 32 may be
substantially homogeneous, and may include portions of first target
material 30, portions of second target material 32, and/or at least
one product formed from reaction of portions of first target
material 30 and second target material 32.
[0064] The operating power of energy source 28 and the division of
energy delivered from energy source 28 to first target material 30
and second target material 32 may vary based on, for example, the
chemical compositions of first target material 30 and second target
material 32, the desired composition of the layer to be formed from
first target material 30 and second target material 32 (e.g., the
composition of an EBC 14), and the configuration of vapor
deposition chamber 24. In the illustrated example of FIG. 2, where
energy source 28 directs first energy beam 36 to first target
material 30 and directs second energy beam 38 to second target
material 32, energy source 28 may utilize operating parameters
which result in formation of an EBC including a rare earth silicate
on target substrate 26. For example, energy source 28 may be an
electron beam gun that operates at a power between approximately 5
KW and approximately 50 KW. In some embodiments, energy source 28
may operate at a power between approximately 10 KW and
approximately 30 KW, or between approximately 12.5 KW and
approximately 25 KW.
[0065] In some embodiments, energy source 28 may direct relative
amounts of energy to produce a vapor phase composition of first
target material 30 and a vapor phase composition of second target
material 32 which is substantially similar to the desired
composition of the layer to be deposited on target substrate 26. As
described above, first target material 30 may and second target
material 32 may have a different vapor pressure, and thus a
different rate of vaporization, at a similar temperature and
pressure. Hence, when energy source 28 delivers a similar amount of
energy to first target material 30 and second target material 32,
this may not cause similar amounts of first target material 30 and
second target material 32 to vaporize. Similarly, when energy
source 28 delivers a specified ratio of energy to first target
material 30 and second target material 32, this may not cause a
similar ratio of first target material 30 and second target
material 32 to vaporize. Accordingly, energy source 28 may deliver
a ratio of energy to first target material 30 and second target
material 32 to cause vaporization a desired ratio of first target
material 30 and second target material 32.
[0066] For example, in some embodiments in which first target
material 30 includes a rare earth oxide and second target material
32 includes silica, energy source 28 may deliver to first target
material 30 between approximately 50% and approximately 75% of the
total energy delivered to first and second target materials 30, 32
and may deliver to second target material 32 between approximately
25% and approximately 50% of the total energy delivered. In other
examples, energy source 28 may deliver to first target material 30
between approximately 52.5% and approximately 62.5% of the total
energy delivered to first and second target materials 30, 32, or
between approximately 56.5% and approximately 59.5% of the total
energy delivered to first and second target materials 30, 32.
Energy source 28 may direct the remaining amount of energy to
second target material 32.
[0067] The amount of energy delivered to first target material 30
and second target material 32 may be controlled by controlling, for
example, a relative amount of time for which energy source 28
directs first energy beam 36 onto first target material 30 and
second energy beam 38 onto second target material 32, a relative
power of first energy beam 36 and second energy beam 38, or the
like. In cases where energy source 28 delivers energy at a
substantially constant rate, the relative amount of energy directed
to first target material 30 and second target material 32 may be
equivalent to a residence time for energy delivery to each target
material 30, 32. In other words, when energy source 28 delivers
energy at a substantially constant rate, the amount of time that
energy source 28 directs first energy beam 36 onto first target
material 30 versus the amount of time that energy source 28 directs
second energy beam 38 onto second target material 32 may be
equivalent to the energy ratio between the two target materials 30,
32. In some examples, energy source 28 may direct first energy beam
36 onto first target material 30 between approximately 52.5% and
approximately 62.5% of the total time that energy is being
delivered to first and second target materials 30, 32, while energy
source 28 may direct second energy beam onto second target material
32 between approximately 37.5% and approximately 47.5% of the total
amount of time that energy is delivered to first and second target
materials 30, 32.
[0068] As will be appreciated, the relative amount of energy
delivered by energy source 28 to first target material 30 and
second target material 32 may vary based on, for example, the
number of target materials 30, 32, the composition of the target
materials 30, 32, and/or the number of energy sources in vapor
deposition chamber 24. Accordingly, energy delivery may be
characterized as a ratio of energy delivered to first target
material 30 to energy delivered to second target material 32. In
some examples, the ratio may be between approximately 1:1 and
approximately 3:1, such as between approximately 1.1:1 and
approximately 1.7:1 or between approximately 1.33:1 and
approximately 1.47:1.
[0069] In addition, different parameters may be controlled within
vapor deposition chamber 24 to form different EBC microstructures.
An EBC may exhibit a substantially nonporous dense microstructure
or a columnar microstructure, as discussed with respect to FIG. 1.
Parameters that may be adjusted to control the microstructure of an
EBC include, but are not necessarily limited to, the temperature of
target substrate 26 and the rate at which target substrate 26
rotates within vapor deposition chamber 24. In some examples, a
substrate temperature less than approximately 1000.degree. C., such
as, e.g., a substrate temperature less than approximately
975.degree. C. may result in a dense microstructure EBC.
Conversely, a substrate temperature greater than approximately
1000.degree. C., such as, e.g., a substrate temperature greater
than approximately 1100.degree. C. may result in a columnar
microstructure EBC. In some examples, rotating target substrate 26
at a rate of less than 10 revolutions per minute, such as, e.g.,
less than 5 revolutions per minute may result in a dense
microstructure. Conversely, rotating target substrate 26 at a rate
greater than 10 revolutions per minute, such as, e.g., greater than
18 revolutions per minute may result in a columnar
microstructure.
[0070] In some examples, at least one of a substrate temperature
and a substrate rotation rate parameter may be controlled to
produce an EBC with either a dense microstructure or a columnar
microstructure, while in other examples, both a substrate
temperature and a substrate rotation rate parameter may controlled
together to produce an EBC with either a dense microstructure or a
columnar microstructure. Values other than those presented above
are contemplated, however, and it should be appreciated that
parameters leading to either a dense microstructure or a columnar
microstructure may vary, e.g., based on the specific target
materials being used and the configuration of the specific vapor
deposition chamber being used.
[0071] Vapor deposition chamber 24 may be used to form EBCs of
different thicknesses. In general, a thickness of an EBC is
measured in the X direction shown in FIG. 1. In some examples, a
thickness of an EBC is less than approximately 100 mils (i.e., 0.1
inches or 2.54 millimeters). For example, a thickness of an EBC may
be between approximately 1 mil (approximately 0.0254 millimeters)
and approximately 10 mils (approximately 0.254 millimeters). Other
thicknesses are possible, however, and the disclosure is not
limited in this regard.
[0072] By using the techniques described herein, one or more layers
can be coated onto a substrate. FIG. 3 is a cross-sectional
schematic diagram of a substrate 42 coated with an example of a
multi-layered EBC 44. Article 40 includes substrate 42.
Multi-layered EBC 44 is formed over a first surface 54 of substrate
42. In the example illustrated in FIG. 3, multi-layered EBC 44
includes first EBC layer 46, second EBC layer 48, third EBC layer
50, and fourth EBC layer 52. One or more of EBC layers 46, 48, 50,
and 52 (collectively, (EBC layers 46'') can be formed using vapor
deposition chamber 24 (FIG. 2). Each EBC layer 46 may be formed
from similar EBC materials or dissimilar EBC materials. Further,
each EBC layer 46 may have a similar microstructure or a dissimilar
microstructure.
[0073] As an example, first EBC layer 46 may have a dense
microstructure that may substantially prevent an environmental
species, such as water vapor, from contacting first surface 54 of
substrate 42. Second EBC layer 48 may have a columnar
microstructure that offers mechanical compliance, sintering
resistance, and/or thermal protection. Third substrate layer 50 may
be another dense microstructure layer to provide protection to
substrate 42 from environmental species. Fourth substrate layer 52
may be another columnar microstructure for mechanical compliance
and/or thermal protection. In this manner, a multilayered EBC 44
may be constructed to address different operating conditions that a
coated substrate 42 may experience.
[0074] At least some of EBC layers 46, 48, 50, 52 may be deposited
using the techniques discussed above with respect to FIG. 2 using
vapor deposition chamber 24. For example, EBC layers 46, 48, 50,
and 52 may all be deposited from one or more target materials
disposed in vapor deposition chamber 24. In some embodiments,
layers 46, 48, 50 and 52 may be deposited sequentially in a
substantially continuous deposition process. That is, layers 46,
48, 50, and 52 may be continuously formed by in-situ changing of
operating parameters of energy source 28 and/or by redirecting
energy source 28 to different target materials to form layers 46,
48, 50, and 52. The layers 46, 48, 50, 52 may also be deposited
discontinuously. For example, first EBC layer 46 may be initially
formed, the deposition process may be paused to, e.g., change
energy source 28 operating parameters, redirect energy source 28 to
different target materials, or to subject first EBC layer 46 to a
post-deposition heat treatment. Second EBC layer 48 may then be
formed on first EBC layer 46.
[0075] In some embodiments, different EBC layers 46, 48, 50, 52 of
article 40 may be deposited using different techniques, one or more
of which utilizes techniques described with reference to FIG. 2 and
vapor deposition chamber 24. For example, first EBC layer 46 may be
deposited using plasma spraying, a slurry process, or CVD. Second
EBC layer 48 may then be deposited using a technique described with
reference to FIG. 2 and vapor deposition chamber 24. Third EBC
layer 50 and fourth EBC layer 52 may then be deposited using, for
example, vapor deposition chamber 24 or one or more of the
techniques used to deposit first EBC layer 46.
[0076] Although article 40 is shown with four adjacently positioned
EBC layers 46, 48, 50, 52, it should be appreciated that EBC 44 may
include a different number of layers, ranging from a single layer
to a plurality of layers. The specific number of EBC layers 46, 48,
50, 52 may depend on the conditions in which substrate 42 will
operate, the thickness and chemical composition of each EBC layer
46, 48, 50, 52, or other performance considerations.
[0077] In some embodiments, a high-temperature mechanical system
component may receive additional coating layers beyond the EBC or
EBC layer(s) discussed above (e.g., EBC 14 of FIG. 1A, first EBC
layer 16 and second EBC layer 18 of FIG. 1B, or EBC layers 46, 48,
50, 52 of FIG. 3). As an example, a substrate may receive a bond
coat layer in addition to an EBC. The bond coat may promote
adhesion between layers or between the substrate and a layer. In
some situations, a bond coat may enhance the adherence of an EBC to
a substrate, thereby improving the durability of the article over
its service life.
[0078] FIG. 4 is a cross-sectional diagram of an article 60 that
includes a bond coat layer. Specifically, article 60 includes
substrate 62. A bond coat 64 is formed over a first surface 68 of
substrate 62. An EBC 66 is further formed over bond coat 64.
[0079] As noted, bond coat 64 may promote adhesion between layers
underlying and overlying bond coat 64, e.g., between substrate 62
and EBC 66. Bond coat 64 may include ceramics or other materials
that are compatible with an underlying layer and an overlying
layer. For example, when substrate 62 includes a ceramic or CMC,
bond coat 64 may include silicon, mullite, a rare earth oxide, or
combinations thereof. In some examples, bond coat 64 includes an
additive. For example, suitable additives include silicon,
silicides, alkali metal oxides, alkali earth metal oxides, mullite,
glass ceramics, Al.sub.2O.sub.3, TiO.sub.2, Ta.sub.2O.sub.5,
HfO.sub.2, ZrO.sub.2, HfSiO.sub.4, HfTiO.sub.4, ZrTiO.sub.4, or
combinations thereof.
[0080] Bond coat 64 may be formed to any suitable thickness, such
as a thickness that facilitates adhesion between substrate 62 and
EBC 66 to provide protection to article 60 as described herein. For
example, bond coat 64 may have thickness between approximately 0.1
mils (approximately 0.00254 millimeters; 1 mil=0.001 inch) and
approximately 5 mils (approximately 0.127 millimeters). In some
cases, bond coat 64 may have thickness between approximately 0.5
mils (approximately 0.0127 millimeters) and approximately 5 mils
(approximately 0.127 millimeters), such as between approximately 1
mils (approximately 0.0254 millimeters) and approximately 4 mils
(approximately 0.1016 millimeters), or between approximately 2 mil
(approximately 0.0508 millimeters) and approximately 4 mils
(approximately 0.1016 millimeters).
[0081] Although shown as a single layer, in some examples, bond
coat 64 includes multiple layers. In some implementations, a bond
coat 64 that includes multiple layers may be desirable because each
layer may provide different characteristics to the multilayer bond
coat 64. For example, one bond coat layer may promote adhesion
between substrate 62 and EBC 66. Continuing the example, another
bond coat layer may provide chemical compatibility between
substrate 62 and EBC 66.
[0082] Additionally or alternatively, multiple bond coat layers may
provide thermal expansion grading. For example, different bond coat
layers may exhibit different thermal expansion coefficients. A bond
coat layer near substrate 62 may have a thermal expansion
coefficient similar to substrate 62 while a bond coat layer near
EBC 66 may have a thermal expansion coefficient similar to EBC 66.
An intermediate bond coat layer may have a thermal expansion
coefficient that is between the thermal expansion coefficient of
the bond coat layer near substrate 62 and the thermal expansion
coefficient of the bond coat layer near EBC 66. In this manner,
different bond coat layers can compensate for different
coefficients of thermal expansion exhibited by substrate 62 and EBC
66.
[0083] Bond coat 64 may be applied to substrate 62 using any
suitable deposition technique. For example, bond coat 64 may be
applied to substrate 62 using vapor deposition chamber 24 (FIG. 2).
Alternatively, bond coat 64 may be applied to substrate 62 using
other techniques, such as plasma spraying, a slurry process, or
CVD.
[0084] Although bond coat 64 may be applied to substrate 62,
article 60 may not always include bond coat 64. EBC 66 may be
applied on substrate 62 without bond coat 64. In some cases, an
additive may be directly incorporated into EBC 66 to increase
adherence between EBC 66 and substrate 62 or another layer formed
between substrate 62 and EBC 66. Examples of suitable additives
include silicon, silicides, alkali metal oxides, alkali earth metal
oxides, mullite, Al.sub.2O.sub.3, TiO.sub.2, Ta.sub.2O.sub.5,
HfO.sub.2, ZrO.sub.2, ZrSiO.sub.4, HfSiO.sub.4, HfTiO.sub.4,
ZrTiO.sub.4, glass ceramics (including, for example, barium
strontium alumina silicate
(BaO.sub.x--SrO.sub.1-x--Al.sub.2O.sub.3-2SiO.sub.2), a barium
alumina silicate (BaO--Al.sub.2O.sub.3-2SiO.sub.2), a strontium
alumina silicate (SrO--Al.sub.2O.sub.3-2SiO.sub.2), a calcium
alumina silicate (CaO--Al.sub.2O.sub.3-2SiO.sub.2), a magnesium
alumina silicate (2MgO-2Al.sub.2O.sub.3-5SiO.sub.2), and a lithium
alumina silicate (Li.sub.2O--Al.sub.2O.sub.3-2SiO.sub.2)), and
combinations thereof. In some examples, EBC 66 may include a rare
earth silicate and an additive selected from the group consisting
of Al.sub.2O.sub.3, TiO.sub.2, Ta.sub.2O.sub.5, HfSiO.sub.4,
ZrSiO.sub.4, alkali metal oxides, alkali earth metal oxides, and
combinations thereof. As another example, EBC 66 may include a rare
earth alumino silicate.
[0085] In some embodiments, EBC 66 may include between
approximately 5 weight percent and 60 weight percent additive
material, such as between approximately 35 weight percent 55 weight
percent additive material. For example, EBC 66 may include greater
than or equal to approximately 50 weight percent rare earth
silicate and less than or equal to approximately 50 weight percent
additive. Regardless of the specific amount of additive, EBC 66
that includes an additive may be any thickness suitable to provide
protection to substrate 62. For instance, an EBC 66 that includes
an additive may fall within the range of EBC thicknesses discussed
above.
[0086] EBC 66 may include any composition and microstructure
described herein with reference to other EBCs or EBC layers. For
example, EBC 66 may include a rare earth silicate, a rare earth
oxide, and/or silica. In some embodiments, EBC 66 may include at
least one additive, as described above. Additionally, EBC 66 may
include a substantially porous microstructure or a columnar
microstructure.
[0087] Although article 60 is depicted in FIG. 4 as including an
EBC 66 formed in a single layer, in other embodiments, an article
may include a bond coat 64 and an EBC 66 including more than one
layer. For example, an article may include a bond coat 64 formed on
substrate 62 and a multilayer EBC, such as EBC 15 illustrated in
FIG. 1B or EBC 44 illustrated in FIG. 3. Additionally or
alternatively, an article may include a bond coat 64 formed on
substrate 62, an single layer or multilayer EBC formed on bond coat
64, and, optionally, an overlay coating, as will be described below
with reference to FIG. 6. Any suitable methods may be used to
incorporate additive material into EBC 66. In some cases, an
additive material may be deposited by using at least one target
material in vapor deposition 24 (FIG. 2). The at least one target
material may include at least a first target material that includes
a rare earth oxide, a second target material that includes silica,
and a third target material that includes an additive material.
[0088] FIG. 5 is a schematic diagram of a vapor deposition chamber
80 for coating substrate 26 using a plurality of different target
materials. As illustrated, vapor deposition chamber 80 encloses
target substrate 26, first energy source 82, and second energy
source 84. First energy source 82 is positioned to direct an
electron beam toward a portion of a first target material 86 and
toward a portion of a third target material 90. Second energy
source 84 is positioned to direct an electron beam toward a portion
of a second target material 88 and toward a portion of the third
target material 90.
[0089] Vapor deposition chamber 80 may be substantially similar to
or the same as vapor deposition chamber 24 and may be used in
similar or the same configurations and under similar or the same
operating conditions. For example, vapor deposition chamber 80 may
be used for EB-PVD or DVD. In some examples, vapor deposition
chamber 80 may operate at vacuum conditions or near vacuum
conditions that are generated through vacuum port 34. Further,
substrate 26 may be coupled to a stage 25 which rotates in one or
more directions during the vapor deposition process to ensure
uniform coating of the substrate 26.
[0090] In some embodiments, first energy source 82 and/or second
energy source 84 may be an electron beam source. The electron beam
sources may operate within the same range of parameters discussed
above with respect to energy source 28. Although two energy sources
82, 84 are shown in FIG. 5 and each energy source is direct toward
a pair of different target materials 86, 88, 90 (e.g., first energy
source 82 is directed to first target material 86 and third target
material 90 and second energy source 84 is directed to second
target material 88 and third target material 90), in further
examples, a different number or different configuration of energy
sources 82, 84 may be used. The specific number and specific
configuration of energy sources 82, 84 within a deposition chamber
80 that includes a plurality of target materials 86, 88, 90 may
vary depending, for example, on desired coating rates, number of
target materials 86, 88, 90 utilized, composition of target
materials 86, 88, 90, or the like. For example, a single energy
source may be used alone, as illustrated with respect to FIG. 2.
The single energy source may be variably directed toward each of
the various target materials 86, 88, 90 disposed within deposition
chamber 80. In further examples, each target material 86, 88, 90
may have a dedicated energy source that operates only to a vaporize
target material 86, 88, 90 assigned to the dedicated energy source.
Regardless, vapor deposition chamber 80 may be used to vaporize
target materials 86, 88, and 90, thereby creating an EBC that
includes an additive.
[0091] Aside from the different number of energy sources 82, 84 and
different number of target materials 86, 88, 90, vapor deposition
chamber 80 may operate similarly to vapor deposition chamber 24
described with reference to FIG. 2. For example, energy sources 82,
84 may operate with parameters similar to energy source 28,
including power, scanning rate, residence times, or the like. Of
course, depending on the composition of target materials target
materials 86, 88, 90, first energy source 82 and/or second energy
source 84 may operate with parameters different from those
described with respect to energy source 28. In any case, the
operating parameters of vapor deposition chamber 80 and energy
sources 82, 84 may be selected to produce a coating having a
desired composition, microstructure, and thickness. For example,
the operating parameters of vapor deposition chamber 80 and energy
sources 82, 84 may be selected to produce an EBC including a rare
earth aluminosilicate from a first target material 86 including a
rare earth oxide, a second target material 88 including silica, and
a third target material 90 including alumina. As described above,
the operating parameters for energy sources 82, 84 may be selected
based on, for example, relative heats of vaporization or relative
vapor pressures of components of target materials 86, 88, 90, a
desired composition of the coating to be formed on target substrate
26, or the like.
[0092] Additionally, in some embodiments, first energy source 82
and second energy source 84 may direct respective energy beams at
first target material 86, second target material 88, and third
target material 90 in a manner which leads to deposition of
portions of target materials 86, 88, 90 on target substrate 26 in a
single layer. In such embodiments, vaporized portions of the target
materials 86, 88, 90 may be considered to be substantially
simultaneously deposited on target substrate 26. In some
embodiments, this may indicate that portions of target materials
86, 88, 90 mix when deposited to form a layer on target substrate
26, e.g., portions of the target materials 86, 88, 90 form a single
layer instead of a plurality of sub-layers of material from first
target material 86, second target material 88, and third target
material 90, respectively. In some embodiments, the layer deposited
from target materials 86, 88, 90 may be substantially homogeneous,
and may include portions of first target material 86, portions of
second target material 88, portions of third target material 90,
and/or a product formed from reaction of portions of first target
material 86, second target material 88, and/or third target
material 90.
[0093] Beyond the coatings described above, a substrate for a
high-temperature mechanical system component may sometimes receive
different or additional coating layers. For example, a substrate
for a high-temperature mechanical system component may receive an
overlay coating.
[0094] FIG. 6 is a cross-sectional diagram of an article 100 that
includes an overlay coating 106. Article 100 includes EBC 104
formed over substrate 102. Overlay coating 106 is further formed
over EBC 104. In the illustrated example, EBC 104 includes first
EBC layer 108 and second EBC layer 110.
[0095] Substrate 102 may include, for example, a superalloy, a
ceramic, CMC, or metal-silicon alloy. Substrate 102 may include any
composition suitable for use in a high-temperature mechanical
component, including, for example, any composition described
herein.
[0096] EBC 104, and first EBC layer 108 and second EBC layer 110,
may include any of the compositions described herein. In some
examples, at least one of first EBC layer 108 or second EBC layer
110 may include a rare earth silicate, a rare earth oxide, and/or
silica. In some examples the composition of first EBC layer 108 and
second EBC layer 110 is substantially similar or the same. In other
examples, the composition of first EBC layer 108 and second EBC
layer 110 is different.
[0097] In some embodiments, at least one of first EBC layer 108 or
second EBC layer 110 may be deposited over substrate 102 using a
vapor deposition technique described herein, e.g., with reference
to vapor deposition chamber 24 of FIG. 2 or vapor deposition
chamber 80 of FIG. 5.
[0098] As described above with reference to FIG. 1B, in some
examples, first EBC layer 108 may include a dense, substantially
nonporous microstructure and second EBC layer 110 may include a
columnar microstructure. In other examples, second EBC layer 110
may include a dense, substantially nonporous microstructure and
first EBC layer 108 may include a columnar microstructure. In still
other examples, first EBC layer 108 and second EBC layer 110
include a similar microstructure, which may be either substantially
nonporous or columnar.
[0099] Although FIG. 6 illustrates EBC 104 as including first EBC
layer 108 and second EBC layer 110, in other embodiments, EBC 104
may include a single layer or more than two layers. Other example
constructions which EBC 104 may include are described with respect
to FIGS. 1A and 1B, FIG. 3, FIG. 4, and FIG. 7.
[0100] In some embodiments, overlay coating 106 includes a
CMAS-resistant overlay coating. A CMAS-resistant overlay coating
may provide protection from chemical attack of EBC 104 and/or
substrate 102 by CMAS deposits or physical infiltration of pores in
underlying layers by CMAS. These types of deposits can form, for
example, in a gas turbine engine when siliceous minerals such as
dust, sand, volcanic ashes, runway debris, and the like are
ingested into the engine with intake air. In some cases, the gas
turbine engine may operate at temperatures above the melting point
of components of CMAS, which may allow molten CMAS to infiltrate
the pores or cracks of an underlying layer, such as second EBC
layer 110 and/or first EBC layer 108. Infiltration of pores or
cracks by CMAS may be particularly pernicious when an EBC layer
108, 110 is not substantially nonporous because the pores or cracks
of the EBC layer 108, 110 may be larger in this configuration.
Regardless, when a component is cooled below the CMAS melting
temperature, the CMAS solidifies, which may exert strain on the
infiltrated layer and reduce the service life of the coated article
100. CMAS-resistant layer 106 may help prevent infiltration of
pores of second EBC layer 110 and/or first EBC layer 108 by CMAS
deposits. Additionally or alternatively, CMAS-resistant layer 106
may reduce or substantially prevent chemical reaction between CMAS
and a component of second EBC layer 110 and/or first EBC layer 108,
which also may serve to reduce service life of article 100.
[0101] An overlay coating 106 which provides CMAS-resistance may
include any materials that are useful for mitigating effects of
CMAS. Examples of suitable materials may include a rare earth
oxide, silica, alumina (Al.sub.2O.sub.3), an alkali oxide, an
alkali earth oxide, TiO.sub.2, Ta.sub.2O.sub.5, and HfSiO.sub.4, or
combinations thereof. For example, one or more rare earth oxides
may be combined with alumina to form overlay coating 106. As
another example, one or more rare earth oxides may be combined with
alumina and silica to form overlay coating 106. A further
combination for overlay coating 106 may include one or more rare
earth oxides together with alumina, silica, and a component
selected from the group consisting of alkali oxides, alkali earth
oxides, TiO.sub.2, Ta.sub.2O.sub.5, and HfSiO.sub.4.
[0102] The thickness of overlay coating 106 may vary widely
depending on the conditions under which article 100 is to be used.
For example, if overlay coating 106 provides CMAS resistance and
CMAS deposits are expected to be extensive, overlay coating 106 may
be thicker than if CMAS deposits are not expected to be extensive.
Additionally, the thickness of overlay coating 106 may vary
depending on the operating environment (e.g., debris and
temperatures) to which article 100 will be subject. Depending on
the particular application, the thickness of overlay coating 106
may be between approximately 0.1 mils and approximately 60 mils. In
some cases, the thickness of overlay coating 106 may be between
approximately 0.1 mils and approximately 30 mils, such as between
approximately 0.5 mils and approximately 15 mils.
[0103] In addition to, or instead of, a CMAS-resistant layer,
overlay coating 106 may include a thermal barrier overlay coating
(TBC). As discussed, TBCs may improve the performance of
high-temperature mechanical system components by providing thermal
insulation and may even allow a component to operate in an elevated
temperature envelop. In some cases, EBC 104 may itself provide some
thermal insulation to substrate 102. For instance, an EBC 104
including a rare earth silicate and having a columnar
microstructure may exhibit characteristics consistent with a TBC.
In other cases, however, a separate overlay 106 coating which is a
TBC may be beneficially applied to EBC 104.
[0104] An overlay coating 106 including a TBC layer may include any
materials that provide thermal protection for a high-temperature
component. In some examples, overlay coating 106 may include a
material and/or microstructure which results in the coating 106
exhibiting a relatively low effective coefficient of thermal
conductivity (k). For example, overlay coating 106 may include
yttria-stabilized zirconia (YSZ) compounds, compounds of zirconia
stabilized by one or more rare earth oxides, zirconia-rare earth
oxide compounds (such as RE.sub.2Zr.sub.2O.sub.7 where RE
represents a rare earth element), compounds of hafnia stabilized by
one or more rare earth oxides, hafnia-rare earth oxide compounds
(such as RE.sub.2Hf.sub.2O.sub.7 where RE represents a rare earth
element), rare earth silicate compounds (such
RE.sub.2Si.sub.2O.sub.7, RE.sub.2SiO.sub.5 where RE represents a
rare earth element), or combinations thereof.
[0105] The thickness of an overlay coating 106 including a TBC
layer may vary depending on the specific TBC materials to be
employed, the material structure of substrate 102, the composition
and microstructure of EBC 104, and/or the operating conditions in
which article 100 will be utilized. For example, if article 100 is
expected to be used in a higher temperature envelope, overlay
coating 106 may be thicker. Additionally, the thickness of overlay
coating 106 may vary depending on the operating conditions under
which article 100 is expected to be used. Depending on the
particular application, the thickness of overlay coating 106 may
range from between approximately 100 and 500 micrometers.
[0106] Overlay coating 106 may be applied using any suitable
techniques. For example, a CMAS-resistant layer, a TBC layer, or
both may be applied using vapor deposition chamber 24, 80. The
different target materials in vapor deposition chamber 24, 80 may
include the different constituent components of overlay coating
106. Alternatively, overlay coating 106 may be applied other EB-PVD
or DVD methods, which rely on a single source of target material.
In further examples, overlay coating 106 may be deposited using a
CVD process, plasma spraying, or a slurry process.
[0107] When a CMAS-resistant layer or a TBC layer is formed using
vapor deposition chamber 24, 80, the CMAS-resistant layer and/or
the TBC layer may exhibit a dense, substantially nonporous
microstructure or a columnar microstructure. Example techniques for
creating a layer with a dense microstructure and a layer with a
columnar microstructure are described above. These example
techniques can be employed when creating a CMAS-resistant layer
and/or a TBC layer.
[0108] Although CMAS-resistant coatings and TBC coatings are
described in relation to overlay coating 106 for ease of
description, a CMAS-resistant coating and/or a TBC coating need not
be the outermost layer of article 100. In different examples, a
CMAS-resistant coating and/or a TBC coating may be directly
adjacent substrate 102 or interposed between various layers. For
example, an article may include a substrate, an EBC layer formed
over substrate, a CMAS-resistant layer formed over the EBC layer,
and a TBC layer formed over the CMAS-resistant layer. In other
examples, an article may include a substrate, an EBC layer formed
over the substrate, a TBC layer formed over the EBC layer, and a
CMAS-resistant layer formed over the TBC layer. In other
embodiments, a CMAS-resistant coating and/or a TBC coating may even
be interposed between two layers of a multi-layer EBC, e.g., EBC
104.
[0109] As discussed, a high-temperature mechanical system component
may include multiple coating layers formed over a surface of the
component. For example, a component may include an EBC, alone or in
combination with at least one of a bond coat, a CMAS-resistant
layer, a TBC layer, and combinations thereof. In some examples, a
component may include additional layers. For example, one or more
compositional transition layers may be formed between different
coating layers, e.g., between an EBC layer and a CMAS-resistant
layer, between an EBC layer and a TBC layer, and/or between a
CMAS-resistant layer and a TBC layer. The one or more compositional
transition layers may function to provide chemical and/or
mechanical compatibility between the layers. For example, the one
or more compositional transition layers may provide thermal
expansion grading to compensate for the different coefficients of
thermal expansion between different layers.
[0110] FIG. 7 is a cross-sectional schematic diagram of an example
article 120 that includes different coating layers. Article 120
includes substrate 122, such as a silicon-based ceramic matrix
composite substrate. Bond coat 124 is formed over substrate 122,
and EBC 126 is formed over bond coat 124. EBC 126 includes first
EBC layer 128, second EBC layer 130, and third EBC layer 132.
Compositional transition layer 134 is formed between third EBC
layer 132 and CMAS-resistant layer 128. CMAS-resistant layer 128
forms the outermost layer for article 120.
[0111] Compositional transition layer 134 may function by providing
compositional steps between layers of different materials. For
example, compositional transition layer 134 may include materials
from different adjacent layers that sandwich the compositional
transition layer 134 (e.g., third EBC layer 132 and CMAS-resistant
layer 128), thus providing a compositional transition between two
layers. Further, as described, a compositional transition may be a
single layer or may include multiple layers. For instance, article
120 may include three compositional transition layers between third
EBC layer 132 and CMAS-resistant layer 128. Each compositional
transition layer may include components that are used to form third
EBC layer 132 and components that are used to form CMAS-resistant
layer 128. A first compositional transition layer adjacent to third
EBC layer 132 may include more components that are used to form
third EBC layer 132 than components that are used to form
CMAS-resistant layer 128. A second compositional transition layer
may include an even blend (e.g., 50/50 mol percent ratio) of
components used to form third EBC layer 132 and components used to
form CMAS-resistant layer 128. A third compositional transition
layer adjacent CMAS-resistant layer 128 may include more components
that are used to form CMAS-resistant layer 128 than components that
are used to form third EBC layer 132. In this manner, one or more
compositional transition layers may provide compositional grading
between layers of different materials.
[0112] Compositional transition layer 134 may be formed using any
suitable techniques. For example, compositional transition layer
134 may be formed using vapor deposition chamber 24, 80. Target
materials that are used to form the different layers between
compositional transition layer 134 (e.g., third EBC layer 132 and
CMAS-resistant layer 128) can be provided in vapor deposition
chamber 24, 80. By controlling the vaporization rates of the
different target materials, the specific composition of
compositional transition layer 134 can be controlled and
adjusted.
[0113] Compositional transition layer 134 can be deposited so the
compositional transition layer 134 exhibits a dense, substantially
nonporous microstructure or a columnar microstructure. Different
example techniques for creating a layer with a dense microstructure
versus a layer with a columnar microstructure are described above.
The example techniques can be employed when creating compositional
transition layer 134. For example, an article may include an EBC
with a dense, substantially nonporous microstructure, a
compositional transition layer formed over the EBC layer that
exhibits a columnar microstructure, and a CMAS-resistant layer
formed over the compositional transition layer that also exhibits a
columnar microstructure. As another example, an article may include
an EBC with a dense, substantially nonporous microstructure, a
compositional transition layer formed over the EBC layer that
exhibits a columnar microstructure, and two CMAS-resistant layers
formed over the compositional transition layer, one of which
exhibits a columnar microstructure and one of which exhibits a
dense, substantially nonporous microstructure. The CMAS-resistant
layer with the dense microstructure may be sandwiched between the
columnar microstructure layers of the compositional transitional
layer and the CMAS-resistant layer. Alternatively, the
CMAS-resistant layer with the dense microstructure may form a top
layer of an article.
[0114] While different numbers, types and configurations of layers
have been described with respect to specific figures, it should be
appreciated that this disclosure is not limited to the specific
examples described and illustrated. Aspects of the various
described examples may be combined, modified, or eliminated to
produce hybrid layered structures beyond those explicitly discussed
herein. For example, any of the EBCs described herein may be used
in combination with at least one of a bond coat, a CMAS-resistant
layer, a TBC, and/or at least one compositional transition
layer.
[0115] The following examples provide additional details of some
examples of EBCs and coating techniques in accordance with this
disclosure.
EXAMPLES
Example 1
[0116] FIGS. 8A and 8B show examples of two x-ray diffraction
patterns for different ytterbium disilicate
(Yb.sub.2Si.sub.2O.sub.7) materials. FIG. 8A is an x-ray
diffraction pattern for an ytterbium disilicate power. FIG. 8B is
an x-ray diffraction pattern for an EBC including ytterbium
disilicate formed over a substrate. The ytterbium silicate EBC was
formed using a DVD process that included two target materials. The
first target material was an ingot that included ytterbium oxide.
The second target material was an ingot that included silica. The
similarity between the two x-ray diffraction patterns indicates
that the EBC formed using the DVD process included ytterbium
disilicate formed from reaction between ytterbium oxide and
silica.
Example 2
[0117] FIG. 9 is a micrograph of an example of an article 150 that
includes a ytterbium silicate EBC 152. EBC 152 was formed over
substrate 150 using a DVD process that included two target
materials. The first target material was an ingot that included
ytterbium oxide. The second target material was an ingot that
included silica. EBC 150 exhibits a dense microstructure that is
substantially nonporous.
Example 3
[0118] FIG. 10 is a micrograph of an example of an article 160 that
includes a ytterbium silicate EBC 162. EBC 162 was formed over
substrate 160 using a DVD process that included two target
materials. The first target material was an ingot that included
ytterbium oxide. The second target material was an ingot that
included silica. EBC 162 includes columns 164 separated by gaps
165. Columns 164 and gaps 165 define a columnar microstructure for
EBC 162.
Example 4
[0119] FIG. 11 is a cross-sectional image of an article 170.
Article 170 includes a ytterbium silicate environmental barrier
coating 174 formed over substrate 172. Substrate 172 is a ceramic
matrix composite substrate that includes a silicon carbide (SiC)
ceramic and a silicon carbide filler material. Environmental
barrier coating 174 was formed over substrate 172 using a directed
vapor deposition process that included two target materials. The
first target material was an ingot that included ytterbium oxide.
The second target material was an ingot that included silica.
[0120] Article 170 was subject to 100 hours of thermal cycling with
1 hour cycles in an atmosphere with a partial pressure of water
equal to 0.9 atmospheres prior to capturing FIG. 11. The thermal
and moisture cycling were designed to simulate a combustion
environment in a turbine engine. As illustrated, environmental
barrier coating 174 exhibited no cracking, no delamination, and
only minimal oxidation. Thus, FIG. 11 indicates that environmental
barrier coatings formed using the materials and techniques
described herein may be used to suitably protect a high temperature
mechanical system component from high temperature cycling and
reactive chemical species attack.
Example 5
[0121] FIG. 12 is a cross-sectional image of an article 180 that
includes a dual microstructure environmental barrier coating.
Article 180 includes gadolinium silicate columnar microstructure
environmental barrier coating 186 formed over a ytterbium silicate
dense microstructure environmental barrier coating 184. Further,
dense microstructure environmental barrier coating 184 is formed
over substrate 182. Substrate 182 is a ceramic matrix composite
substrate that includes a silicon carbide (SiC) ceramic and a
silicon carbide filler material. Environmental barrier coatings 184
and 186 were both formed using a directed vapor deposition process
that included two target materials. Environmental barrier coating
184 was formed from a first target material that was an ingot that
included ytterbium oxide and a second target material that was an
ingot that included silica. Environmental barrier coating 186 was
formed from a third target material was an ingot that included
gadolinium oxide and a fourth target material that was an ingot
that included silica.
[0122] Like article 170 in FIG. 11 above, article 180 was subject
to 100 hours of thermal cycling with 1 hour cycles in an atmosphere
with a partial pressure of water equal to 0.9 atmospheres prior to
capturing FIG. 12. The thermal and moisture cycling were designed
to simulate a combustion environment in a turbine engine. As
illustrated, environmental barrier coatings 184 and 186 exhibited
no cracking, no delamination, and only minimal oxidation. FIG. 12
further indicates that environmental barrier coatings formed using
the materials and techniques described herein may be used to
suitably protect a high temperature mechanical system component
from high temperature cycling and reactive chemical species
attack.
Example 6
[0123] In this example, a ytterbium di-silicate environmental
barrier coating was formed in a directed vapor deposition chamber
that included a single electron beam energy source. The directed
vapor deposition chamber included a first target material
comprising ytterbium oxide and a second target material comprising
silica. The target substrate was heated to approximately 970
degrees Celsius and rotated at 3 revolutions per minute to produce
an environmental barrier coating that included a portion with a
dense microstructure. The target substrate was then heated to
approximately 1125 degrees Celsius and rotated at 20 revolutions
per minute to produce an environmental barrier coating that include
a portion with columnar microstructure. The electron beam energy
source operated at approximately 22 kilowatts, and the electron
beam was alternated between the first target material and the
second target material at rate between approximately 5 and 10
kilohertz. As a result, the electron beam resided on the ytterbium
oxide target material for approximately 58 percent of the
deposition time while the electron beam only resided on the silica
target material for approximately 42 percent of the deposition
time.
[0124] The electron beam source was operated for approximately 35
minutes. Afterwards, the different target materials were weighted
to determine the composition of the environmental barrier coating
on the substrate. The electron beam source removed approximately
150 grams of ytterbium oxide from the first target material and
approximately 130 grams of silica from the second target material,
resulting in an evaporated mass ratio of ytterbium silicate to
silica of approximately 1.14.
Example 7
[0125] Similar to Example 6, this example involved forming an
environmental barrier coating in a directed vapor deposition
chamber that included a single electron beam energy source. Unlike
Example 6, however, this example focused on forming a gadolinium
mono-silicate environmental barrier coating. The directed vapor
deposition chamber included a first target material comprising
gadolinium oxide and a second target material comprising silica.
The target substrate was heated to approximately 1040 degrees
Celsius and rotated at 3 revolutions per minute. The electron beam
energy source operated at approximately 15 kilowatts, and the
electron beam was alternated between the first target material and
the second target material at rate between approximately 5 and 10
kilohertz. As a result, the electron beam resided on the gadolinium
oxide target material for approximately 59 percent of the
deposition time while the electron beam only resided on the silica
target material for approximately 41 percent of the deposition
time.
[0126] The electron beam source was operated for approximately 30
minutes. Afterwards, the different target materials were weighted
to determine the composition of the environmental barrier coating
on the substrate. The electron beam source removed approximately 75
grams of gadolinium oxide from the first target material and
approximately 50 grams of silica from the second target material,
resulting in an evaporated mass ratio of ytterbium silicate to
silica of approximately 1.52.
[0127] Various examples have been described. These and other
embodiments are within the scope of the following claims.
* * * * *