U.S. patent application number 15/343076 was filed with the patent office on 2017-05-11 for plasma spray physical vapor deposition deposited environmental barrier coating.
The applicant listed for this patent is Rolls-Royce Corporation. Invention is credited to Matthew R. Gold, Kang N. Lee.
Application Number | 20170130313 15/343076 |
Document ID | / |
Family ID | 57223573 |
Filed Date | 2017-05-11 |
United States Patent
Application |
20170130313 |
Kind Code |
A1 |
Gold; Matthew R. ; et
al. |
May 11, 2017 |
PLASMA SPRAY PHYSICAL VAPOR DEPOSITION DEPOSITED ENVIRONMENTAL
BARRIER COATING
Abstract
A technique may include controlling, by a computing device, a
vacuum pump to evacuate a vacuum chamber to high vacuum. The
technique also may include controlling, by the computing device, a
coating material source to provide a coating material to a plasma
spray device, the coating material having a first composition
including a first amount of a metal oxide and a second amount of
silica. The second amount of silica may be greater than an amount
of silica in a metal silicate including the first amount of metal
oxide. The technique further may include controlling, by the
computing device, the plasma spray device to deposit an
environmental barrier coating on a substrate in the vacuum chamber
using plasma spray physical vapor deposition, wherein the coating
comprises the metal silicate.
Inventors: |
Gold; Matthew R.; (Carmel,
IN) ; Lee; Kang N.; (Strongsville, OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Rolls-Royce Corporation |
Indianapolis |
IN |
US |
|
|
Family ID: |
57223573 |
Appl. No.: |
15/343076 |
Filed: |
November 3, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62252121 |
Nov 6, 2015 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C23C 28/04 20130101;
C04B 41/5024 20130101; F23R 3/002 20130101; F01D 11/00 20130101;
C23C 4/10 20130101; C04B 41/009 20130101; C23C 4/134 20160101; F05D
2230/90 20130101; C23C 14/22 20130101; C04B 41/5024 20130101; C23C
14/32 20130101; C04B 41/87 20130101; F01D 9/02 20130101; F05D
2300/21 20130101; F05D 2220/32 20130101; C23C 4/11 20160101; C04B
35/806 20130101; C04B 41/4533 20130101; C04B 41/5035 20130101; C04B
35/565 20130101; C04B 41/5031 20130101; C04B 41/009 20130101; C23C
14/08 20130101; F01D 5/288 20130101; C23C 14/548 20130101 |
International
Class: |
C23C 4/11 20060101
C23C004/11; C23C 28/04 20060101 C23C028/04; C23C 4/134 20060101
C23C004/134 |
Claims
1. A system comprising: a vacuum pump; a vacuum chamber; a plasma
spray device; a coating material source; and a computing device
operable to: control the vacuum pump to evacuate the vacuum chamber
to high vacuum; control the coating material source to provide a
coating material to the plasma spray device, the coating material
having a first composition including a first amount of a metal
oxide and a second amount of silica, wherein the second amount of
silica is greater than an amount of silica in a metal silicate
including the first amount of metal oxide; and control the plasma
spray device to deposit an environmental barrier coating on a
substrate in the vacuum chamber using plasma spray physical vapor
deposition, wherein the coating comprises the metal silicate.
2. The system of claim 1, wherein the metal oxide comprises at
least one of alumina, barium oxide, strontium oxide, or a rare
earth oxide.
3. The system of claim 1, wherein the metal oxide comprises a rare
earth oxide, and wherein the metal silicate comprises at least one
of a rare earth monosilicate or a rare earth disilicate.
4. The system of claim 3, wherein the coating material further
comprises alumina, and wherein the environmental barrier coating
further comprises alumina.
5. The system of claim 1, wherein the computing device is
configured to control the plasma spray device to deposit the
environmental barrier coating with a substantially dense
microstructure.
6. The system of claim 1, wherein the computing device is
configured to control the plasma spray device to deposit the
environmental barrier coating with a columnar microstructure.
7. The system of claim 1, wherein the computing device is
configured to control the plasma spray device to deposit a first
layer of the environmental barrier coating with a substantially
dense microstructure and a second layer of the environmental
barrier coating with a columnar microstructure.
8. The system of claim 1, wherein the environmental barrier coating
is deposited on at least one surface of the substrate that is not
in a line-of-sight relationship with the plasma spray gun.
9. A method comprising: controlling, by a computing device, a
vacuum pump to evacuate a vacuum chamber to high vacuum;
controlling, by the computing device, a coating material source to
provide a coating material to a plasma spray device, the coating
material having a first composition including a first amount of a
metal oxide and a second amount of silica, wherein the second
amount of silica is greater than an amount of silica in a metal
silicate including the first amount of metal oxide; and
controlling, by the computing device, the plasma spray device to
deposit an environmental barrier coating on a substrate in the
vacuum chamber using plasma spray physical vapor deposition,
wherein the environmental barrier coating comprises the metal
silicate.
10. The method of claim 9, wherein the metal oxide comprises at
least one of alumina, barium oxide, strontium oxide, or a rare
earth oxide.
11. The method of claim 9, wherein the metal oxide comprises a rare
earth oxide, and wherein the metal silicate comprises at least one
of a rare earth monosilicate or a rare earth disilicate.
12. The method of claim 11, wherein the coating material further
comprises alumina, and wherein the environmental barrier coating
further comprises alumina.
13. The method of claim 9, wherein the computing device is
configured to control the plasma spray device to deposit the
environmental barrier coating with at least one of a substantially
dense microstructure or a columnar microstructure.
14. The method of claim 9, wherein the computing device is
configured to control the plasma spray device to deposit a first
layer of the environmental barrier coating with a substantially
dense microstructure and a second layer of the environmental
barrier coating with a columnar microstructure.
15. The method of claim 9, wherein the environmental barrier
coating is deposited on at least one surface of the substrate that
is not in a line-of-sight relationship with the plasma spray
gun.
16. A computer readable storage device comprising instructions
that, when executed, cause a computing device to: control a vacuum
pump to evacuate a vacuum chamber to high vacuum; control a coating
material source to provide a coating material to a plasma spray
device, the coating material having a first composition including a
first amount of a metal oxide and a second amount of silica,
wherein the second amount of silica is greater than an amount of
silica in a metal silicate including the first amount of metal
oxide; and control the plasma spray device to deposit an
environmental barrier coating on a substrate in the vacuum chamber
using plasma spray physical vapor deposition, wherein the coating
comprises the metal silicate.
17. The computer readable storage device of claim 16, wherein the
metal oxide comprise a rare earth oxide, and wherein the metal
silicate comprises at least one of a rare earth monosilicate or a
rare earth disilicate.
18. The computer readable storage device of claim 16, wherein the
instructions, when executed, cause the computing device to control
the plasma spray device to deposit the environmental barrier
coating with at least one of a substantially dense microstructure
or a columnar microstructure.
19. The computer readable storage device of claim 16, wherein the
instructions, when executed, cause the computing device to control
the plasma spray device to deposit a first layer of the
environmental barrier coating with a substantially dense
microstructure and a second layer of the environmental barrier
coating with a columnar microstructure.
20. The computer readable storage device of claim 16, wherein the
instructions, when executed, cause the computing device to control
the plasma spray device the environmental barrier coating on at
least one surface of the substrate that is not in a line-of-sight
relationship with the plasma spray gun.
Description
[0001] This application claims the benefit of U.S. Provisional
Application No. 62/252,121 filed Nov. 6, 2015, which is
incorporated herein by reference in its entirety.
TECHNICAL FIELD
[0002] The disclosure relates to techniques for forming
environmental barrier coatings using plasma spray physical vapor
deposition.
BACKGROUND
[0003] Ceramic or ceramic matrix composite (CMC) materials may be
useful in a variety of contexts where mechanical and thermal
properties are important. For example, components of high
temperature mechanical systems, such as gas turbine engines, may be
made from ceramic or CMC materials. Ceramic or CMC materials may be
resistant to high temperatures, but some ceramic or CMC materials
may react with some elements and compounds present in the operating
environment of high temperature mechanical systems, such as water
vapor. Reaction with water vapor may result in the recession of the
ceramic or CMC material. These reactions may damage the ceramic or
CMC material and reduce mechanical properties of the ceramic or CMC
material, which may reduce the useful lifetime of the component.
Thus, in some examples, a ceramic or CMC material may be coated
with an environmental barrier coating, which may reduce exposure of
the substrate to elements and compounds present in the operating
environment of high temperature mechanical systems.
SUMMARY
[0004] In some examples, the disclosure described a system that
includes a vacuum pump, a vacuum chamber, a plasma spray device, a
coating material source, and a computing device. The computing
device may be configured to control the vacuum pump to evacuate the
vacuum chamber to high vacuum. The computing device also may be
configured to control the coating material source to provide a
coating material to the plasma spray device, the coating material
having a first composition including a first amount of a metal
oxide and a second amount of silica. The second amount of silica
may be greater than an amount of silica in a metal silicate
including the first amount of metal oxide. Further, the computing
device may be configured to control the plasma spray device to
deposit an environmental barrier coating on a substrate in the
vacuum chamber using plasma spray physical vapor deposition,
wherein the coating includes the metal silicate.
[0005] In some examples, the disclosure describes a method that
includes controlling, by a computing device, a vacuum pump to
evacuate a vacuum chamber to high vacuum. The method also may
include controlling, by the computing device, a coating material
source to provide a coating material to a plasma spray device, the
coating material having a first composition including a first
amount of a metal oxide and a second amount of silica. The second
amount of silica may be greater than an amount of silica in a metal
silicate including the first amount of metal oxide. Additionally,
the method may include controlling, by the computing device, the
plasma spray device to deposit an environmental barrier coating on
a substrate in the vacuum chamber using plasma spray physical vapor
deposition, wherein the coating includes the metal silicate.
[0006] In some examples, the disclosure describes a computer
readable storage device including instructions that, when executed,
cause a computing device to control a vacuum pump to evacuate a
vacuum chamber to high vacuum. The computer readable storage device
also may include instructions that, when executed, cause the
computing device to control a coating material source to provide a
coating material to a plasma spray device, the coating material
having a first composition including a first amount of a metal
oxide and a second amount of silica. The second amount of silica
may be greater than an amount of silica in a metal silicate
including the first amount of metal oxide. Further, the computer
readable storage device may include instructions that, when
executed, cause the computing device to control the plasma spray
device to deposit an environmental barrier coating on a substrate
in the vacuum chamber using plasma spray physical vapor deposition,
wherein the coating includes the metal silicate.
[0007] The details of one or more examples are set forth in the
accompanying drawings and the description below. Other features,
objects, and advantages will be apparent from the description and
drawings, and from the claims.
BRIEF DESCRIPTION OF DRAWINGS
[0008] FIG. 1 is a conceptual and schematic diagram illustrating an
example system for forming a coating that includes an environmental
barrier coating including a metal silicate using plasma spray
physical vapor deposition.
[0009] FIG. 2 is a conceptual block diagram illustrating an example
article including a substrate and a coating that includes an
environmental barrier coating including a first, substantially
dense layer, and a second, columnar layer.
[0010] FIG. 3 is a flow diagram illustrating an example technique
for forming a coating that includes an environmental barrier
coating including a metal silicate using plasma spray physical
vapor deposition.
[0011] FIG. 4 is a scatter diagram illustrating an example
relationship between excess silica in a coating material and an
amount of silicon in a resulting coating.
[0012] FIG. 5 is a cross-sectional picture of an example coating
deposited using PS-PVD as described in this disclosure.
[0013] FIG. 6 is a cross-sectional picture of an example coating
deposited using PS-PVD as described in this disclosure.
[0014] FIG. 7 is a cross-sectional picture of an example coating
deposited using PS-PVD as described in this disclosure.
DETAILED DESCRIPTION
[0015] The disclosure describes systems and techniques for forming
an environmental barrier coating (EBC) including a metal silicate
using plasma spray physical vapor deposition (PS PVD). In some
examples, PS PVD may be used to deposit a coating material
including silica and a rare earth oxide (RE.sub.2O.sub.3), where RE
is Lu (lutetium), Yb (ytterbium), Tm (thulium), Er (erbium), Ho
(holmium), Dy (dysprosium), Tb (terbium), Gd (gadolinium), Eu
(europium), Sm (samarium), Pm (promethium), Nd (neodymium), Pr
(praseodymium), Ce (cerium), La (lanthanum), Y (yttrium), or Sc
(scandium). The silica and rare earth oxide react to form the rare
earth silicate. Rare earth silicates include rare earth
monosilicates (RE.sub.2SiO.sub.5, where RE is a rare earth element)
and rare earth disilicates (RE.sub.2Si.sub.2O.sub.7, where RE is a
rare earth element). Rare earth silicates have different physical
and chemical properties than a mechanical mixture of rare earth
oxide and silica.
[0016] Silica and rare earth oxides may have different physical or
chemical properties that make simultaneous deposition difficult.
For example, silica may have a higher vapor pressure than a rare
earth oxide at a given temperature and pressure, which results in
silica being more likely to be lost via volatilization during the
processing, resulting in less silicon condensing on a surface of a
substrate in the EBC. Thus, when PS PVD is used to deposit a rare
earth silicate from a single material source, the resulting EBC may
have a different composition than the material source
composition.
[0017] If a material source includes a stoichiometric amount of
rare earth oxide and silica to form a rare earth monosilicate, the
silica deficit in the deposited coating may result in excess rare
earth oxide, which may form a second phase in the EBC and provides
different properties to the EBC than rare earth monosilicate.
Similarly, if a material source includes a stoichiometric amount of
rare earth oxide and silica to form a rare earth disilicate, the
silica deficit in the coating may result in excess rare earth
monosilicate forming in the EBC, which may form a second phase in
the EBC, and provides different properties to the EBC than rare
earth disilicate. For example, when a composition of an EBC
deviates from an intended chemical composition, environmental and
thermal forces may degrade the EBC more quickly than predicted
based on the intended composition. In some cases, the failure of
the EBC may lead to the failure of the component coated with the
EBC due to damage of the underlying substrate. Hence, if a
particular rare earth silicate is desired in the EBC, control of
the amount of rare earth oxide and silica in the material source is
important to achieve that type of rare earth silicate in the EBC.
Similar effects may occur for other metal silicates.
[0018] Described herein are techniques for depositing EBCs
including metal silicates. In some examples, the EBCs may include
substantially stoichiometric ratio of silica to metal oxide. In
this way, in some examples, the EBC may include substantially no
(e.g., no or nearly no) free silica, or substantially no free metal
oxide. The techniques may include depositing the EBC from a coating
material including a predetermined amount of excess silica. The
amount of excess silica may be selected based on experimental or
theoretical relationships between the amount of silica in the
coating material and the amount of silica (e.g., within the metal
silicate) in the resulting EBC.
[0019] FIG. 1 is a conceptual and schematic diagram illustrating an
example system 10 for forming a coating 18 including an EBC that
includes a metal silicate using PS PVD. System 10 includes a vacuum
chamber 12, which encloses a stage 14, and a plasma spray device
20. System 10 also includes a vacuum pump 24, a coating material
source 26, and a computing device 22. A substrate 16 is disposed in
enclosure 12 and includes coating 18.
[0020] Vacuum chamber 12 may substantially enclose (e.g., enclose
or nearly enclose) stage 14, substrate 16, and plasma spray device
20. Vacuum chamber 12 is fluidically connected to at least one
vacuum pump 24, which is operable to pump fluid (e.g., gases) from
the interior of vacuum chamber 12 to establish a vacuum in vacuum
chamber 12. In some examples, vacuum pump 24 may include multiple
pumps or multiple stages of a pump, which together may evacuate
vacuum chamber 12 to high vacuum. For example, vacuum pump 24 may
include at least one of a scroll pump, a screw pump, a roots pump,
a turbomolecular pump, or the like. As used herein, high vacuum may
refer to pressures of less than about 10 torr (about 1.33
kilopascals (kPa)). In some examples, the pressure within vacuum
chamber 12 during the PS-PVD technique may be between about 0.5
torr (about 66.7 pascals) and about 10 torr (about 1.33 kPa).
[0021] In some examples, during the evacuation process, vacuum
chamber 12 may be backfilled with a substantially inert atmosphere
(e.g., helium, argon, or the like), then the substantially inert
gases removed during subsequent evacuation to the target pressure
(e.g., high vacuum). In this way, the gas molecules remaining in
vacuum chamber 12 under high vacuum may be substantially inert,
e.g., to substrate 16 and coating 18.
[0022] In some examples, stage 14 may be configured to selectively
position and restrain substrate 16 in place relative to stage 14
during formation of coating 18. In some examples, stage 14 is
movable relative to plasma spray device 20. For example, stage 14
may be translatable and/or rotatable along at least one axis to
position substrate 16 relative to plasma spray device 20.
Similarly, in some examples, plasma spray device 20 may be movable
relative to stage 14 to position plasma spray device 20 relative to
substrate 16.
[0023] Plasma spray device 20 includes a device used to generate a
plasma 28 for use in the PS PVD technique. For example, plasma
spray device 20 may include a plasma spray gun including a cathode
and an anode separated by a plasma gas channel. As the plasma gas
flows through the plasma gas channel, a voltage may be applied
between the cathode and anode to cause the plasma gas to form the
plasma 28. In some examples, the coating material may be injected
inside plasma spray device 20 such that the coating material flows
through part of the plasma gas channel. In some examples, the
coating material may be introduced to the plasma external to plasma
spray device 20, as shown in FIG. 1. In some examples, the coating
material may be a relatively fine powder (e.g., an average particle
size of less than about 5 micrometers) to facilitate vaporization
of the coating material by the plasma. In some examples, the
relatively fine powder may be agglomerated into a composite powder
that serves as the material fed to plasma spray device 20. The
composite powder may have a particle size that is larger than the
relatively fine powder.
[0024] Coating material source 26 may include at least one source
of material which is injected into the plasma 28 generated by
plasma spray device 20 and deposited in coating 18 on substrate 16.
In some examples, the material may be in powder form, and may be
supplied by coating material source 26 carried by a fluid, such as
air, an inert gas, or the like.
[0025] In some examples, the coating includes an EBC including a
metal silicate. The coating material may include particles of a
metal monosilicate or a metal disilicate. In some examples, the
coating material may include particles including a metal oxide,
particles that include silica, or both, where the particles
including metal oxide are separate from the particles including
silica, and are mechanically mixed in a powder mixture. In other
examples, the particles including metal oxide may be agglomerated
with particles including silica to form larger particles. For
example, particles of metal oxide and particles of silica may be
mixed and agglomerated such that the agglomerated particles include
a ratio of moles of metal oxide to moles of silica in an
approximately stoichiometric amount for the selected type of
silicate (e.g., a metal monosilicate or a metal disilicate).
[0026] In accordance with some examples of this disclosure, the
coating material may include excess silica compared to the desired
amount of silica in coating 18 (e.g., in the monosilicate or
disilicate). In some examples, the excess silica may be mixed in
the coating material as a separate powder. In other examples, the
excess silica may be part of an agglomerate with the metal
oxide.
[0027] The excess silica in the coating source may facilitate
formation of an EBC with a desired composition. As described above,
silica may have a higher vapor pressure than some other metal
oxides, such as rare earth oxides, at a given pressure and
temperature. This may result in silica being more likely to be lost
via volatilization during the processing, such that silica deposits
in coating 18 in a lower ratio than the ratio of silica in the
coating material. Thus, by including excess silica in a
predetermined amount, coating 18 may be formed with a desired
amount of silica. For example, the excess amount of silica may be
selected such that the ratio of silica to metal oxide deposited in
coating 18 is substantially the same as a stoichiometric ratio of
the desired metal silicate (e.g., a monosilicate or a disilicate).
In other examples, the amount of silica in the coating material may
be selected to result in a predetermined amount of excess silica or
excess rare earth oxide in coating 18 compared to a stoichiometric
ratio of metal oxide to silica in the desired metal silicate. This
may result in a selected amount of free silica or free metal oxide
in coating 18.
[0028] The amount of excess silica included in the coating material
may depend on the desired composition of coating 18, and may be
based on experimental testing. For example, a first coating
material having a first ratio of silica to metal oxide may be
formed and a coating deposited from the coating material using PS
PVD. The composition of the resulting coating may be determined,
and the ratio of silica to metal oxide (e.g., in the form of a
metal silicate) in the coating may be compared to the ratio of
silica to metal oxide in the coating material. This process may be
repeated to determine an amount of excess silica to include in the
coating material to form coating 18 with a desired composition.
[0029] In some examples, additional and optional constituents of
coating 18 may be included in the coating material or another
coating material used to deposit coating 18. For example, the
additional and optional constituents may include alumina, an alkali
metal oxide, an alkaline earth metal oxide, TiO.sub.2,
Ta.sub.2O.sub.5, HfSiO.sub.4, or the like.
[0030] Computing device 22 may include, for example, a desktop
computer, a laptop computer, a workstation, a server, a mainframe,
a cloud computing system, or the like. Computing device 22 may
include or may be one or more processors, such as one or more
digital signal processors (DSPs), general purpose microprocessors,
application specific integrated circuits (ASICs), field
programmable logic arrays (FPGAs), or other equivalent integrated
or discrete logic circuitry. Accordingly, the term "processor," as
used herein may refer to any of the foregoing structure or any
other structure suitable for implementation of the techniques
described herein. In addition, in some examples, the functionality
of computing device 22 may be provided within dedicated hardware
and/or software modules.
[0031] Computing device 22 is configured to control operation of
system 10, including, for example, stage 14, plasma spray device
20, and/or vacuum pump 24. Computing device 22 may be
communicatively coupled to at least one of stage 14, plasma spray
device 20, and/or vacuum pump 24 using respective communication
connections. Such connections may be wireless and/or wired
connections.
[0032] Computing device 22 may be configured to control operation
of stage 14 and/or plasma spray device 20 to position substrate 16
relative to plasma spray device 20. For example, as described
above, computing device 22 may control plasma spray device 20 to
translate and/or rotate along at least one axis to position
substrate 16 relative to plasma spray device 20.
[0033] As described above, system 10 may be configured to perform a
PS PVD technique to deposit coating 18 on substrate 16. In some
examples, substrate 16 may include component of a high temperature
mechanical system, such as a gas turbine engine. For example,
substrate 16 may be part of a seal segment, a blade track, an
airfoil, a blade, a vane, a combustion chamber liner, or the like.
In some examples, substrate may include a ceramic or a CMC. Example
ceramic materials may include, for example, silicon carbide (SiC),
silicon nitride (Si.sub.3N.sub.4), alumina (Al.sub.2O.sub.3),
aluminosilicate, silica (SiO.sub.2), transition metal carbides and
silicides (e.g. WC, Mo.sub.2C, TiC, MoSi.sub.2, NbSi.sub.2,
TiSi.sub.2), or the like. In some examples, substrate 16
additionally may include silicon metal, carbon, or the like. In
some examples, substrate 16 may include mixtures of two or more of
SiC, Si.sub.3N.sub.4, Al.sub.2O.sub.3, aluminosilicate, silica,
silicon metal, carbon, or the like.
[0034] In examples in which substrate 16 includes a CMC, substrate
16 includes a matrix material and a reinforcement material. The
matrix material includes a ceramic material, such as, for example,
silicon metal, SiC, or other ceramics described herein. The CMC
further includes a continuous or discontinuous reinforcement
material. For example, the reinforcement material may include
discontinuous whiskers, platelets, fibers, or particulates. As
other examples, the reinforcement material may include a continuous
monofilament or multifilament weave. In some examples, the
reinforcement material may include SiC, C, other ceramic materials
described herein, or the like. In some examples, substrate 16
includes a SiC--SiC ceramic matrix composite.
[0035] Coating 18 may include an environmental barrier coating
(EBC) and, optionally, at least one other layer. For example,
coating 18 may include a bond coat and an EBC. A bond coat may
include, for example, silicon metal, alone, or mixed with at least
one other constituent. For example, a bond coat may include silicon
metal and at least one of a transition metal carbide, a transition
metal boride, a transition metal nitride, mullite (aluminum
silicate, Al.sub.6Si.sub.2O.sub.13), silica, a silicide, an oxide
(e.g., silicon oxide, a rare earth oxide, an alkali oxide, or the
like), a silicate (e.g., a rare earth silicate or the like), or the
like. In some examples, the additional constituent(s) may be
substantially homogeneously mixed with silicon metal. In other
examples, the additional constituent(s) may form a second phase
distinct from the silicon metal phase.
[0036] Coating 18 also includes an EBC, alone or in addition to the
bond coat. In examples in which coating 18 includes the EBC in
addition to a bond coat, the EBC may be on the bond coat. The EBC
may include constituents and a physical construction selected to
reduce contact of underlying layers with chemical species present
in the environment in which substrate 16 is used, such as water
vapor, calcia-magnesia-alumina-silicate (CMAS; a contaminant that
may be present in intake gases of gas turbine engines), or the
like. The EBC may include at least one metal silicate, such as at
least one rare earth silicate. For example, the EBC may include at
least one metal monosilicate, such as at least one rare earth
monosilicate (RE.sub.2SiO.sub.5, where RE is a rare earth element),
at least one metal disilicate, such as at least one rare earth
disilicate (RE.sub.2Si.sub.2O.sub.7, where RE is a rare earth
element), or combinations thereof. Rare earth elements include Lu,
Yb, Tm, Er, Ho, Dy, Tb, Gd, Eu, Sm, Pm, Nd, Pr, Ce, La, Y, or Sc.
As described above, rare earth silicates may be formed by reaction
of silica and a rare earth oxide.
[0037] In some examples, the EBC additionally and optionally may
include at least one additive, such as at least one of silica, a
rare earth oxide, alumina, an aluminosilicate, an alkali metal
oxide, an alkaline earth metal oxide, an alkali metal
aluminosilicate, an alkaline earth aluminosilicate, TiO.sub.2,
Ta.sub.2O.sub.5, HfSiO.sub.4, or the like. The additive may be
added to the EBC to modify one or more desired properties of the
EBC. For example, the additive components may increase or decrease
the reaction rate of the EBC with calcia-magnesia-alumina-silicate
(CMAS; a contaminant that may be present in intake gases of gas
turbine engines), may modify the viscosity of the reaction product
from the reaction of CMAS and constituent(s) of the EBC, may
increase adhesion of the EBC to the bond coat, may increase the
chemical stability of the EBC, or the like.
[0038] In some examples, the EBC may be a substantially non-porous
layer (e.g., may include a porosity of less than about 5 volume
percent). A substantially nonporous microstructure may
substantially prevent (e.g., prevent or nearly prevent)
environmental species such as water vapor, oxygen, molten salt, or
calcia-magnesia-alumina-silicate (CMAS) deposits from contacting
substrate 16 and degrading the material structure of substrate 16.
For example, water vapor may react with a substrate 16 including a
CMC and volatilize silica or alumina components in substrate 16.
Consequently, an EBC which is substantially nonporous may provide
protection to substrate 16 by preventing water vapor from
contacting and reacting with substrate 16. In some examples, an EBC
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 EBC
volume.
[0039] In some examples, the EBC may include a columnar
microstructure. A columnar microstructure may have microcracks or
microgaps that extend through at least a portion of the EBC in a
direction that is substantially orthogonal to the plane defined by
the EBC coating surface. 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
having a columnar microstructure may provide improved thermal
protection to substrate 16 compared to an EBC 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 having a columnar microstructure compared to
a substantially nonporous EBC of a similar composition.
[0040] In some examples, thermal protection and mechanical
compliance are not the only benefits of a columnar microstructure
EBC. An EBC having a columnar microstructure may also exhibit
enhanced erosion resistance and enhanced sintering resistance
relative to an EBC that does not include a columnar
microstructure.
[0041] In some examples, coating 18 may include a first EBC layer
and a second EBC layer, as shown in FIG. 2. FIG. 2 is a conceptual
block diagram illustrating an example article 30 including a
substrate 32 and a coating 34 that includes an environmental
barrier coating including a first layer 38, and a second layer 40.
Coating 34 also includes a bond coat 36, which, as described above,
may be optional. In some examples, first EBC layer 38 and second
EBC layer 40 may have different microstructures and/or different
compositions, while in other examples, first EBC layer 38 and
second EBC layer 40 may have similar microstructures and/or similar
compositions. For example, the first EBC layer 38 may include a
columnar microstructure and the second EBC layer 40 may include a
substantially dense microstructure. Conversely, the first EBC layer
38 may include a substantially dense microstructure and the second
EBC layer 40 may include a columnar microstructure.
[0042] With respect to the composition of first EBC layer 38 and
second EBC layer 40, in some examples, first and second EBC layers
38, 40 may include the same constituents in similar proportions. In
other examples, first and second EBC layers 38, 40 may include the
same constituents in different proportions. For example, first EBC
layer 38 may include a rare earth disilicate while second EBC layer
40 may include a rare earth monosilicate. The interface between
first EBC layer 38 and second EBC layer 40 may be discrete, where
there is a sharp compositional or microstructural transition
between first EBC layer 38 and second EBC layer 40. Alternatively,
the interface between first EBC layer 38 and second EBC layer 40
may be compositionally graded, where the interface transitions from
being compositionally similar to first EBC layer 38 adjacent first
EBC layer 38 to being compositionally similar to second EBC layer
40 adjacent to second EBC layer 40.
[0043] Computing device 22 may be configured to control operation
of system 10 (e.g., vacuum pump 24, plasma spray device 20, and
coating material source 26) to perform PS PVD to deposit the EBC.
PS PVD may operate at low operating pressures, such as between
about 0.5 torr and about 10 torr. In some examples, the
temperatures of the plasma may be greater than about 6000 K, which
may vaporize the coating material. Because the vaporized coating
material is carried by a gas stream, PS PVD may allow deposition
coating 18 on surfaces of substrate 16 that are not in
line-of-sight relationship with plasma spray device 20, unlike
thermal spray processes, such as air plasma spraying. Further, a
deposition rate (e.g., thickness of coating deposited per unit
time) may be greater for PS PVD than for other vapor phase
deposition processes, such as chemical vapor deposition or physical
vapor deposition, which may result in PS PVD being a more
economical coating technique.
[0044] Moreover, PS PVD may be used to deposit coatings with
different microstructural configurations, e.g., including a
substantially dense microstructure, a columnar microstructure, or
the like. For example, the rate at which coating material is fed by
coating material source 26 into plasma 28 may affect the amount of
the coating material that is vaporized by plasma 28. A higher rate
of coating material being fed into plasma 28 may reduce the amount
of the coating material that is vaporized by plasma 28. When
substantially all of the coating material is vaporized, the
resulting deposited EBC may be substantially nonporous, while when
less coating material is vaporized, the resulting deposited EBC may
have a columnar microstructure. In this way, a single coating
technique, PS PVD may be used to deposit multiple layers of an EBC
with different microstructures.
[0045] FIG. 3 is a flow diagram illustrating an example technique
for forming a coating that includes an environmental barrier
coating including a metal silicate using plasma spray physical
vapor deposition. The technique of FIG. 3 will be described with
respect to system 10 of FIG. 1 and article 30 of FIG. 2 for ease of
description only. A person having ordinary skill in the art will
recognize and appreciate that the technique of FIG. 3 may be
implemented using systems other than system 10 of FIG. 1, may be
used to form articles other than article 30 of FIG. 2, or both.
[0046] The technique of FIG. 3 may include, controlling, by
computing device 22, vacuum pump 24 to evacuate vacuum chamber 12
to a high vacuum (42). As described above, vacuum pump 24 may be
used to evacuate vacuum chamber 12 to high vacuum, e.g., less than
about 10 torr (about 1.33 kPa), or between about 0.5 torr (about
66.7 pascals) and about 10 torr (about 1.33 kPa). In some examples,
computing device 22 may control vacuum pump 24 and a source of
substantially inert gas (e.g., helium, argon, or the like) to
evacuate vacuum chamber 12 in multiple pump-downs. For example,
computing device 22 may control vacuum pump 24 to evacuate vacuum
chamber 12 of the atmosphere present when substrate 16 is placed in
vacuum chamber 12. Computing device 22 then may control the source
of the substantially inert gas to fill vacuum chamber 12 with the
substantially inert gas. Computing device 22 may control vacuum
pump 24 to evacuate vacuum chamber 12 of the substantially inert
gas (and remaining atmosphere). In some examples, computing device
22 may control the source of the substantially inert gas and vacuum
pump 24 to fill and evacuate vacuum chamber 12 at least one time
(e.g., a plurality of times) to substantially remove reactive gases
from vacuum chamber 12 and leave substantially only inert gases
such as helium, argon, or the like in vacuum chamber 12.
[0047] The technique of FIG. 2 also may include, controlling, by
computing device 22, coating material source 26 to provide a
coating material to plasma spray device 20 (44). As described
above, the coating material may include silica and at least one
metal oxide, such as at least one rare earth oxide. The amount of
the at least one metal oxide and the amount of silica may be
selected so that coating 18 deposited from the coating material
includes a predetermined ratio of the at least one metal oxide and
silica. Due to the differences in vapor pressure between metal
oxides and silica, the ratio of the at least one metal oxide and
silica in the coating material provided by coating material source
26 may include additional silica compared to coating 18, as
described above.
[0048] The excess silica in the coating source may facilitate
formation of an EBC with a desired composition. As described above,
silica may have a higher vapor pressure than some other metal
oxides, such as rare earth oxides, at a given pressure and
temperature. This may result in silica being more likely to be lost
via volatilization during the processing, such that silica deposits
in coating 18 in a lower ratio than the ratio of silica in the
coating material. Thus, by including excess silica in a
predetermined amount, coating 18 may be formed with a desired
amount of silica. For example, the excess amount of silica may be
selected such that the ratio of silica to metal oxide deposited in
coating 18 is substantially the same as a stoichiometric ratio of
the desired metal silicate (e.g., a monosilicate or a disilicate).
In other examples, the amount of silica in the coating material may
be selected to result in a predetermined amount of excess silica or
excess rare earth oxide in coating 18 compared to a stoichiometric
ratio of metal oxide to silica in the desired metal silicate. This
may result in a selected amount of free silica or free metal oxide
in coating 18.
[0049] The amount of excess silica included in the coating material
may depend on the desired composition of coating 18, and may be
based on experimental testing. For example, a first coating
material having a first ratio of silica to metal oxide may be
formed and a coating deposited from the coating material using PS
PVD. The composition of the resulting coating may be determined,
and the ratio of silica to metal oxide (e.g., in the form of a
metal silicate) in the coating may be compared to the ratio of
silica to metal oxide in the coating material. This process may be
repeated to determine an amount of excess silica to include in the
coating material to form coating 18 with a desired composition.
[0050] The technique of FIG. 3 also includes controlling, by
computing device 22, plasma spray device 20 to deposit coating 18
including an EBC on substrate 16 (46). As described above, the EBC
may include a metal silicate formed by reaction of the silica and
the at least one metal oxide. During the PS PVD technique, the
coating material may be introduced into plasma 28, e.g., internally
or externally to plasma spray device 20. In PS PVD, vacuum chamber
12 is at a pressure lower than that used in low pressure plasma
spray. For example, as described above, computing device 22 may
control vacuum pump 24 to evacuate vacuum chamber 12 to a high
vacuum with a pressure of less than about 10 torr (about 1.33 kPa).
In contrast, in low pressure plasma spray, the pressure in a vacuum
chamber is between about 50 torr (about 6.67 kPa) and about 200
torr (about 26.66 kPa). Because of the lower operating pressure,
the plasma may be larger in both length and diameter, and may have
a relatively uniform distribution of temperature and particle
velocity.
[0051] The temperature of plasma 28 may, in some examples, be above
about 6000 K, which may result in vaporization of substantially all
(e.g., all or nearly all) of the coating material, depending upon
the rate of introduction of the coating material to the plasma 28.
Plasma 28 may carry the coating material toward substrate 16, where
the coating material deposits in a layer on substrate 16. Because
the coating material is carried by plasma 28 toward substrate 16,
PS PVD may provide some non line-of-sight capability, depositing
coating material on surfaces that are not in direct line of sight
with plasma spray device 20. This may facilitate forming coating 18
on substrates with more complex geometry (e.g., non-planar
geometry).
[0052] In some examples, during the PS-PVD technique, computing
device 22 may control plasma spray device 20, stage 14, or both to
move plasma spray device 20, substrate 16, or both relative to each
other. For example, computing device 22 may be configured to
control plasma spray device 20 to scan the plasma plume relative to
substrate 16.
[0053] The techniques described in this disclosure may be
implemented, at least in part, in hardware, software, firmware, or
any combination thereof. For example, various aspects of the
described techniques may be implemented within one or more
processors, including one or more microprocessors, digital signal
processors (DSPs), application specific integrated circuits
(ASICs), field programmable gate arrays (FPGAs), or any other
equivalent integrated or discrete logic circuitry, as well as any
combinations of such components. The term "processor" or
"processing circuitry" may generally refer to any of the foregoing
logic circuitry, alone or in combination with other logic
circuitry, or any other equivalent circuitry. A control unit
including hardware may also perform one or more of the techniques
of this disclosure.
[0054] Such hardware, software, and firmware may be implemented
within the same device or within separate devices to support the
various techniques described in this disclosure. In addition, any
of the described units, modules or components may be implemented
together or separately as discrete but interoperable logic devices.
Depiction of different features as modules or units is intended to
highlight different functional aspects and does not necessarily
imply that such modules or units must be realized by separate
hardware, firmware, or software components. Rather, functionality
associated with one or more modules or units may be performed by
separate hardware, firmware, or software components, or integrated
within common or separate hardware, firmware, or software
components.
[0055] The techniques described in this disclosure may also be
embodied or encoded in a computer system-readable medium, such as a
computer system-readable storage medium, containing instructions.
Instructions embedded or encoded in a computer system-readable
medium, including a computer system-readable storage medium, may
cause one or more programmable processors, or other processors, to
implement one or more of the techniques described herein, such as
when instructions included or encoded in the computer
system-readable medium are executed by the one or more processors.
Computer system readable storage media may include random access
memory (RAM), read only memory (ROM), programmable read only memory
(PROM), erasable programmable read only memory (EPROM),
electronically erasable programmable read only memory (EEPROM),
flash memory, a hard disk, a compact disc ROM (CD-ROM), a floppy
disk, a cassette, magnetic media, optical media, or other computer
system readable media. In some examples, an article of manufacture
may comprise one or more computer system-readable storage
media.
EXAMPLES
Example 1
[0056] FIG. 4 is a scatter diagram illustrating an example
relationship between excess silica in a coating material and an
amount of silicon in a resulting coating. The units on the x-axis
of FIG. 4 are weight percent excess silica (SiO.sub.2) in the
coating material. Excess silica is defined with reference to a
stoichiometric amount of silica in the coating material. In this
example, the coating material includes a mixture of silica,
ytterbium disilicate (Yb.sub.2Si.sub.2O.sub.7), and alumina. For
the samples with 5 wt. % excess silica, the mixture included 1 wt.
% alumina and a balance ytterbium disilicate. For the samples with
5 wt. % excess silica, the mixture included 3 wt. % alumina and a
balance ytterbium disilicate. The units on the y-axis of FIG. 4 are
weight percent elemental silicon (Si) in the resulting coating, as
measured by a microprobe. A stoichiometric ytterbium disilicate
would include about 10.9 wt. % silicon. As shown in FIG. 4,
increasing excess silica in the coating material generally
increased the amount of silicon in the resulting coating.
Example 2
[0057] FIG. 5 is a cross-sectional picture of an example coating
deposited using PS-PVD as described in this disclosure. The coating
illustrated in FIG. 5 was deposited from a coating material
including 5 wt. % excess silica, 1 wt. % alumina and a balance
ytterbium disilicate. The PS-PVD parameters included using a He
carrier gas with oxygen introduced into the PS-PVD chamber. The
power was about 119.9 kW, and the coating time was about 12 minutes
and 30 seconds. The coating was applied directly to the substrate
with a line-of-sight relationship. As shown in FIG. 5, with these
conditions, the coating included a columnar microstructure.
Example 3
[0058] FIG. 6 is a cross-sectional picture of an example coating
deposited using PS-PVD as described in this disclosure. The coating
illustrated in FIG. 6 was deposited from a coating material
including 5 wt. % excess silica, 3 wt. % alumina and a balance
ytterbium disilicate. The PS-PVD parameters included using a
carrier gas with oxygen introduced into the PS-PVD chamber. The
power was about 116.6 kW, and the coating time was about 12
minutes. The coating was applied directly to the substrate with a
line-of-sight relationship. As shown in FIG. 6, with these
conditions, the coating included a porous microstructure, including
closed pores that do not extend through the thickness of the
coating.
Example 4
[0059] FIG. 7 is a cross-sectional picture of an example coating
deposited using PS-PVD as described in this disclosure. The coating
illustrated in FIG. 7 was deposited from a coating material
including 5 wt. % excess silica, 3 wt. % alumina and a balance
ytterbium disilicate. The PS-PVD parameters included using a He
carrier gas with no oxygen introduced into the PS-PVD chamber. The
power was about 117.0 kW, and the coating time was about 17 minutes
and 30 seconds. The coating was applied directly to the substrate
with a line-of-sight relationship. As shown in FIG. 7, with these
conditions, the coating included a substantially dense
microstructure.
[0060] Various examples have been described. These and other
examples are within the scope of the following claims.
* * * * *