U.S. patent application number 14/006848 was filed with the patent office on 2014-03-13 for bond layers for ceramic or ceramic matrix composite substrates.
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 | 20140072816 14/006848 |
Document ID | / |
Family ID | 45953239 |
Filed Date | 2014-03-13 |
United States Patent
Application |
20140072816 |
Kind Code |
A1 |
Lee; Kang N. |
March 13, 2014 |
BOND LAYERS FOR CERAMIC OR CERAMIC MATRIX COMPOSITE SUBSTRATES
Abstract
A bond layer may include a composition that may be stable at
temperatures above about 1410.degree. C. An article may include a
substrate, a bond layer formed on the substrate, and an overlayer
formed over the bond layer. In some examples, the bond layer may
include a substantially homogeneous mixture of Si and at least one
of SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2, a rare earth oxide,
ZrSiO.sub.4, TiO.sub.2, Ta.sub.2O.sub.5, B.sub.2O.sub.3, an alkali
metal oxide, or an alkali earth metal oxide. In other examples, the
bond layer may include Si, an alkali metal oxide, and at least one
of SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2, HfO.sub.2, a rare earth
oxide, ZrSiO.sub.4, HfSiO.sub.4, TiO.sub.2, Ta.sub.2O.sub.5,
B.sub.2O.sub.3, or an alkali earth metal oxide. In other examples,
the bond layer may include B.sub.2O.sub.3.
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: |
45953239 |
Appl. No.: |
14/006848 |
Filed: |
March 22, 2012 |
PCT Filed: |
March 22, 2012 |
PCT NO: |
PCT/US2012/030174 |
371 Date: |
November 25, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61466556 |
Mar 23, 2011 |
|
|
|
Current U.S.
Class: |
428/448 ;
427/255.15 |
Current CPC
Class: |
C04B 41/009 20130101;
C04B 41/009 20130101; C04B 41/52 20130101; C23C 28/04 20130101;
C04B 41/52 20130101; C04B 41/52 20130101; C04B 41/89 20130101; C04B
41/52 20130101; F01D 25/005 20130101; C04B 41/5024 20130101; C04B
41/52 20130101; C04B 41/5035 20130101; C04B 41/5031 20130101; C04B
41/522 20130101; C04B 35/806 20130101; C04B 41/5035 20130101; C04B
41/5096 20130101; C04B 41/5045 20130101; C04B 41/5096 20130101;
C04B 41/5006 20130101; C04B 35/584 20130101; C04B 41/522 20130101;
C04B 41/502 20130101; C04B 41/5024 20130101; C04B 35/806 20130101;
C04B 41/522 20130101; C04B 41/5042 20130101; C04B 41/5096 20130101;
C04B 41/5045 20130101; C04B 41/5096 20130101; C04B 41/5027
20130101; C04B 41/5042 20130101; C04B 41/522 20130101; C04B 41/522
20130101; C04B 35/565 20130101; C04B 41/4529 20130101; C04B 41/52
20130101; C04B 41/52 20130101; C04B 41/52 20130101; C04B 41/009
20130101 |
Class at
Publication: |
428/448 ;
427/255.15 |
International
Class: |
F01D 25/00 20060101
F01D025/00 |
Claims
1. An article comprising: a substrate comprising a ceramic, a
ceramic matrix composite (CMC), or a metal alloy that includes Si;
a bond layer formed on the substrate, wherein the bond layer
comprises a substantially homogeneous mixture of Si and at least
one of SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2, a rare earth oxide,
ZrSiO.sub.4, TiO.sub.2, Ta.sub.2O.sub.5, B.sub.2O.sub.3, an alkali
metal oxide, or an alkali earth metal oxide; and at least one of a
thermal barrier coating (TBC), an environmental barrier coating
(EBC), or a calcia-magnesia-alumina-silicate (CMAS)-resistant layer
formed on the bond layer, wherein the bond layer is configured to
increase adhesion between the substrate and the at least one of the
TBC, the EBC, or the CMAS-resistant layer.
2. The article of claim 1, wherein the bond layer consists
essentially of the substantially homogeneous mixture of Si and at
the least one of SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2, a rare
earth oxide, ZrSiO.sub.4, TiO.sub.2, Ta.sub.2O.sub.5,
B.sub.2O.sub.3, an alkali metal oxide, or an alkali earth metal
oxide.
3. (canceled)
4. The article of claim 1, wherein the bond layer comprises a
substantially homogeneous mixture of Si; at least one of SiO.sub.2,
Al.sub.2O.sub.3, ZrO.sub.2, or a rare earth oxide; and at least one
of ZrSiO.sub.4, TiO.sub.2, Ta.sub.2O.sub.5, B.sub.2O.sub.3, an
alkali metal oxide, or an alkali earth metal oxide.
5. (canceled)
6. The article of claim 4, wherein the bond layer comprises up to
about 50 wt. % Si, up to about 99 wt. % of the at least one of
SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2, or a rare earth oxide, and
up to about 20 wt. % of the at least one of ZrSiO.sub.4, TiO.sub.2,
Ta.sub.2O.sub.5, B.sub.2O.sub.3, an alkali metal oxide, or an
alkali earth metal oxide, with a total of 100 wt. %.
7. (canceled)
8. The article of claim 1, wherein the bond layer comprises a
substantially homogeneous mixture of Si; the alkali metal oxide;
and at least one of SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2,
HfO.sub.2, a rare earth oxide, ZrSiO.sub.4, HfSiO.sub.4, TiO.sub.2,
Ta.sub.2O.sub.5, B.sub.2O.sub.3, or these alkali earth metal
oxide.
9. The article of claim 8, wherein consists essentially of Si; the
alkali metal oxide; and the at least one of SiO.sub.2,
Al.sub.2O.sub.3, ZrO.sub.2, HfO.sub.2, a rare earth oxide,
ZrSiO.sub.4, HfSiO.sub.4, TiO.sub.2, Ta.sub.2O.sub.5,
B.sub.2O.sub.3, or an alkali earth metal oxide.
10. (canceled)
11. The article of claim 8, wherein the bond layer comprises up to
about 50 wt. % Si, up to about 20 wt. % of the alkali metal oxide,
and up to about 99 wt. % of the at least one of SiO.sub.2,
Al.sub.2O.sub.3, ZrO.sub.2, HfO.sub.2, a rare earth oxide,
ZrSiO.sub.4, HfSiO.sub.4, TiO.sub.2, Ta.sub.2O.sub.5,
B.sub.2O.sub.3, or an alkali earth metal oxide, with a total of 100
wt. %.
12. The article of claim 8, wherein the bond layer comprises Si; an
alkali metal oxide; at least one of SiO.sub.2, Al.sub.2O.sub.3,
ZrO.sub.2, HfO.sub.2, or a rare earth oxide; and at least one of
ZrSiO.sub.4, HfSiO.sub.4, TiO.sub.2, Ta.sub.2O.sub.5,
B.sub.2O.sub.3, or an alkali earth metal oxide.
13. (canceled)
14. The article of claim 12, wherein the bond layer comprises up to
about 50 wt. % Si; up to about 20 wt. % of the alkali metal oxide;
and up to about 99 wt. % of the at least one of SiO.sub.2,
Al.sub.2O.sub.3, ZrO.sub.2, HfO.sub.2, or a rare earth oxide; and
up to about 20 wt. % of the at least one of ZrSiO.sub.4,
HfSiO.sub.4, TiO.sub.2, Ta.sub.2O.sub.5, B.sub.2O.sub.3, or an
alkali earth metal oxide, with a total of 100 wt. %.
15. (canceled)
16. An article comprising: a substrate comprising a ceramic, a
ceramic matrix composite (CMC), or a metal alloy comprising Si; and
a bond layer formed on the substrate, wherein the bond layer
comprises B.sub.2O.sub.3; and at least one of a thermal barrier
coating (TBC), an environmental barrier coating (EBC), or a
calcia-magnesia-alumina-silicate (CMAS)-resistant layer formed on
the bond layer, wherein the bond layer is configured to increase
adhesion between the substrate and the at least one of the TBC, the
EBC, or the CMAS-resistant layer.
17. The article of claim 16, wherein the bond layer consists
essentially of B.sub.2O.sub.3.
18. (canceled)
19. The article of claim 16, wherein the bond layer comprises up to
about 20 wt. % B.sub.2O.sub.3 and a balance of the at least one of
Si, SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2, HfO.sub.2, a rare earth
oxide, ZrSiO.sub.4, HfSiO.sub.4, TiO.sub.2, Ta.sub.2O.sub.5, an
alkali metal oxide, or an alkali earth metal oxide, with a total of
100 wt. %.
20. The article of claim 16, wherein the bond layer further
comprises Si; at least one of SiO.sub.2, Al.sub.2O.sub.3,
ZrO.sub.2, HfO.sub.2, or a rare earth oxide; and at least one of
ZrSiO.sub.4, HfSiO.sub.4, TiO.sub.2, Ta.sub.2O.sub.5, an alkali
metal oxide, or an alkali earth metal oxide.
21. The article of claim 20, wherein the bond layer comprises up to
about 20 wt. % B.sub.2O.sub.3; up to about 50 wt. % Si; up to about
99 wt. % of the at least one of SiO.sub.2, Al.sub.2O.sub.3,
ZrO.sub.2, HfO.sub.2, or a rare earth oxide; and up to about 20 wt.
% of the at least one of ZrSiO.sub.4, HfSiO.sub.4, TiO.sub.2,
Ta.sub.2O.sub.5, an alkali metal oxide, or an alkali earth metal
oxide, with a total of 100 wt. %.
22. (canceled)
23. A method comprising: forming a bond layer on a substrate
comprising a ceramic, a ceramic matrix composite (CMC), or a metal
alloy comprising Si, wherein the bond layer comprises a
substantially homogeneous mixture of Si and at least one of
SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2, a rare earth oxide,
ZrSiO.sub.4, TiO.sub.2, Ta.sub.2O.sub.5, B.sub.2O.sub.3, an alkali
metal oxide, or an alkali earth metal oxide; and forming at least
one of a thermal barrier coating (TBC), an environmental barrier
coating (EBC), or a calcia-magnesia-alumina-silicate
(CMAS)-resistant layer formed on the bond layer, wherein the bond
layer is configured to increase adhesion between the substrate and
the at least one of the TBC, the EBC, or the CMAS-resistant
layer.
24. The method of claim 23, wherein forming the bond layer on the
substrate comprises forming on the substrate a bond layer
consisting essentially of the substantially homogeneous mixture of
Si and the at least one of SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2, a
rare earth oxide, ZrSiO.sub.4, TiO.sub.2, Ta.sub.2O.sub.5,
B.sub.2O.sub.3, an alkali metal oxide, or an alkali earth metal
oxide.
25. (canceled)
26. The method of claim 23, wherein forming the bond layer on the
substrate comprises: forming a first layer comprising Si over the
substrate, forming a second layer comprising the at least one of
SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2, a rare earth oxide,
ZrSiO.sub.4, TiO.sub.2, Ta.sub.2O.sub.5, B.sub.2O.sub.3, an alkali
metal oxide, or an alkali earth metal oxide over the substrate, and
wherein heat treating the bond layer comprises heat treating the
first layer and the second layer at between about 1350.degree. C.
and about 1500.degree. C. for up to about 10 hours to form the bond
layer.
27. The method of claim 23, wherein forming the bond layer on the
substrate comprising the ceramic, the ceramic matrix composite
(CMC), or the metal alloy comprising Si comprises: forming a bond
layer on the substrate comprising the ceramic, the ceramic matrix
composite (CMC), or the metal alloy including Si, wherein the bond
layer comprises a substantially homogeneous mixture of Si; an
alkali metal oxide; and at least one of SiO.sub.2, Al.sub.2O.sub.3,
ZrO.sub.2, HfO.sub.2, a rare earth oxide, ZrSiO.sub.4, HfSiO.sub.4,
TiO.sub.2, Ta.sub.2O.sub.5, B.sub.2O.sub.3, or an alkali earth
metal oxide.
28-29. (canceled)
30. The method of claim 27, wherein forming the bond layer on the
substrate comprises: forming a first layer comprising Si over the
substrate, forming a second layer comprising the alkali metal oxide
and the at least one of SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2,
HfO.sub.2, a rare earth oxide, ZrSiO.sub.4, HfSiO.sub.4, TiO.sub.2,
Ta.sub.2O.sub.5, B.sub.2O.sub.3, or an alkali earth metal oxide
over the substrate, and wherein heat treating the bond layer
comprises heat treating the first layer and the second layer at
between about 1350.degree. C. and about 1500.degree. C. for up to
about 10 hours to form the layer.
31. The method of claim 27, wherein forming the bond layer on the
substrate comprises: forming a first layer comprising Si over the
substrate, forming a second layer comprising the alkali metal oxide
over the substrate, forming a third layer comprising the at least
one of SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2, HfO.sub.2, a rare
earth oxide, ZrSiO.sub.4, HfSiO.sub.4, TiO.sub.2, Ta.sub.2O.sub.5,
B.sub.2O.sub.3, or an alkali earth metal oxide over the substrate,
and wherein heat treating the bond layer comprises heat treating
the first layer, the second layer, and the third layer at between
about 1350.degree. C. and about 1500.degree. C. for up to about 10
hours to form the bond layer.
32-36. (canceled)
Description
TECHNICAL FIELD
[0001] The disclosure relates to bond layers for ceramic or ceramic
matrix composite substrates.
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.
Typical components of high-temperature mechanical systems include a
Ni or Co-based superalloy substrate.
[0003] 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)-based
substrate, which may allow an increased operating temperature
compared to a component with a superalloy substrate. The CMC-based
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. The EBC also may provide
some thermal insulation to the CMC-based substrate. The EBC may
include a ceramic topcoat, and may be bonded to the substrate by a
bond layer.
SUMMARY
[0004] In general, the disclosure is directed to a bond layer for a
ceramic or CMC-based substrate and articles including a substrate
and a bond layer. In accordance with some aspects of the
disclosure, the bond layer may be capable of use at temperatures
above the upper use temperature of a silicon (Si) bond layer, which
may be about 1350.degree. C. In this way, a bond layer formed in
accordance with aspects of this disclosure may facilitate use of an
article including such a bond layer at higher temperatures than an
article that includes a Si bond layer.
[0005] In some examples, the bond layer may include a substantially
homogenous mixture of Si and at least one of silica (SiO.sub.2),
alumina (Al.sub.2O.sub.3), zirconia (ZrO.sub.2), a rare earth oxide
(RE.sub.2O.sub.3, where RE is a rare earth element: La, Pr, Nd, Pm,
Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, or Sc), zirconium
silicate (ZrSiO.sub.4), titanium oxide (TiO.sub.2), tantalum oxide
(Ta.sub.2O.sub.5), boron oxide (B.sub.2O.sub.3), an alkali metal
oxide (Li.sub.2O, Na.sub.2O, K.sub.2O, Rb.sub.2O, Cs.sub.2O, or
Fr.sub.2O), or an alkali earth metal oxide (BeO, MgO, CaO, SrO,
BaO, or RaO). In other examples, the bond layer may include Si, an
alkali metal oxide, and at least one of SiO.sub.2, Al.sub.2O.sub.3,
ZrO.sub.2, hafnia (HfO.sub.2), a rare earth oxide, ZrSiO.sub.4,
hafnium silicate (HfSiO.sub.4), TiO.sub.2, Ta.sub.2O.sub.5,
B.sub.2O.sub.3, or an alkali earth metal oxide. In other examples,
the bond layer may include B.sub.2O.sub.3.
[0006] In one aspect, the disclosure is directed to an article that
includes a substrate comprising a ceramic, a CMC, or a metal alloy
including Si, and a bond layer formed on the substrate. In
accordance with this aspect of the disclosure, the bond layer
includes a substantially homogeneous mixture of Si and at least one
of SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2, a rare earth oxide,
ZrSiO.sub.4, TiO.sub.2, Ta.sub.2O.sub.5, B.sub.2O.sub.3, an alkali
metal oxide, or an alkali earth metal oxide. The article also may
include at least one of a thermal barrier coating (TBC), an
environmental barrier coating (EBC), or a
calcia-magnesia-alumina-silicate (CMAS)-resistant layer formed on
the bond layer, wherein the bond layer is configured to increase
adhesion between the substrate and the at least one of the TBC, the
EBC, or the CMAS-resistant layer.
[0007] In another aspect, the disclosure is directed to an article
that includes a substrate comprising a ceramic, a CMC, or a metal
alloy including Si, and a bond layer formed on the substrate. In
accordance with this aspect of the disclosure, the bond layer
includes Si; an alkali metal oxide; and at least one of SiO.sub.2,
Al.sub.2O.sub.3, ZrO.sub.2, HfO.sub.2, a rare earth oxide,
ZrSiO.sub.4, HfSiO.sub.4, TiO.sub.2, Ta.sub.2O.sub.5,
B.sub.2O.sub.3, or an alkali earth metal oxide. The article also
may include at least one of a TBC, an EBC, or a CMAS-resistant
layer formed on the bond layer, wherein the bond layer is
configured to increase adhesion between the substrate and the at
least one of the TBC, the EBC, or the CMAS-resistant layer.
[0008] In an additional aspect, the disclosure is directed to an
article that includes a substrate comprising a ceramic, a CMC, or a
metal alloy including Si, and a bond layer formed on the substrate.
In accordance with this aspect of the disclosure, the bond layer
includes B.sub.2O.sub.3. The article also may include at least one
of a TBC, an EBC, or a CMAS-resistant layer formed on the bond
layer, wherein the bond layer is configured to increase adhesion
between the substrate and the at least one of the TBC, the EBC, or
the CMAS-resistant layer.
[0009] In a further aspect, the disclosure is directed to a method
that includes forming a bond layer on a substrate comprising a
ceramic, a CMC, or a metal alloy including Si. In accordance with
this aspect of the disclosure, the bond layer includes a
substantially homogeneous mixture of Si and at least one of
SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2, a rare earth oxide,
ZrSiO.sub.4, TiO.sub.2, Ta.sub.2O.sub.5, B.sub.2O.sub.3, an alkali
metal oxide, or an alkali earth metal oxide.
[0010] In another aspect, the disclosure is directed to a method
that includes forming a bond layer on a substrate comprising a
ceramic, a CMC or a metal alloy including Si. In accordance with
this aspect of the disclosure, the bond layer includes Si; an
alkali metal oxide; and at least one of SiO.sub.2, Al.sub.2O.sub.3,
ZrO.sub.2, HfO.sub.2, a rare earth oxide, ZrSiO.sub.4, HfSiO.sub.4,
TiO.sub.2, Ta.sub.2O.sub.5, B.sub.2O.sub.3, or an alkali earth
metal oxide.
[0011] In another aspect, the disclosure is directed to a method
that includes forming a bond layer on a substrate comprising a
ceramic, a CMC, or a metal alloy including Si. In accordance with
this aspect of the disclosure, the bond layer includes
B.sub.2O.sub.3.
[0012] The details of one or more examples are set forth in the
accompanying drawings and the description below. Other features,
objects, and advantages of the disclosure will be apparent from the
description and drawings, and from the claims.
BRIEF DESCRIPTION OF DRAWINGS
[0013] FIG. 1 is a conceptual cross-sectional diagram that
illustrates an example of an article that includes a bond layer
formed on a substrate and an EBC formed on the bond layer.
[0014] FIG. 2 is a conceptual cross-sectional diagram that
illustrates an example of an article that includes a bond layer
formed on a substrate and a TBC formed on the bond layer.
[0015] FIG. 3 is a conceptual cross-sectional diagram that
illustrates an example of an article that includes a bond layer
formed on a substrate and a calcia-magnesia-alumina-silicate
(CMAS)-resistant layer formed on the bond layer.
[0016] FIG. 4 is a conceptual cross-sectional diagram that
illustrates an example of an article that includes a bond layer
formed on a substrate, an EBC formed on the bond layer, a TBC
formed on the EBC, and a CMAS-resistant layer formed on the
TBC.
[0017] FIG. 5 is a cross-sectional micrograph of an example article
that includes a bond layer formed in accordance with the aspects of
the disclosure.
[0018] FIG. 6 is a cross-sectional micrograph of an example article
50 that includes a bond layer formed in accordance with the aspects
of the disclosure.
DETAILED DESCRIPTION
[0019] In general, the disclosure is directed to a bond layer for a
ceramic or CMC-based substrate and articles including a substrate
and a bond layer. In accordance with some aspects of the
disclosure, the bond layer may be capable of use at temperatures
above the upper use temperature of a Si bond layer. Although the
melting point of pure Si is about 1410.degree. C., the melting
temperature may decrease as Si is contaminated by impurities. In
some examples, impurities may enter the Si bond layer during
formation or use of the article. Because of the lower melting
temperature, an upper use temperature of an article that includes a
Si bond layer may be limited to about 1350.degree. C. in some
examples.
[0020] In some implementations in which the substrate of the
article includes a ceramic or CMC, the ceramic or CMC substrate may
be able to withstand use temperatures of greater than 1350.degree.
C. or even greater than 1410.degree. C. For example, some advanced
CMCs, such as those in which silicon is not included in the matrix
material, may be able to withstand use temperatures of up to about
1482.degree. C. (about 2700.degree. F.). Accordingly, in examples
in which an article includes a bond layer of Si, the bond layer may
limit the upper use temperature to below a temperature which the
substrate is capable of withstanding.
[0021] In some examples, the bond layer compositions of the present
disclosure may be able to withstand temperatures greater than about
1350.degree. C. or greater than about 1410.degree. C. The bond
layer compositions of the present disclosure may thus facilitate
use of an article including the bond layer compositions at
temperatures greater than about 1350.degree. C. or greater than
about 1410.degree. C. The bond layer compositions of the present
disclosure may also provide adherence between the substrate, the
bond layer, and a layer formed on the bond layer.
[0022] FIG. 1 is a conceptual cross-sectional diagram that
illustrates an example of an article 10 that includes a bond layer
14 formed on a substrate 12 and an EBC 16 formed on bond layer 14.
Article 10 is a component of a high temperature mechanical system,
such as, for example, a gas turbine engine or the like. For
example, article 10 may be a turbine blade, a turbine vane, a
turbine blade track, or a combustor liner.
[0023] Substrate 12 may include a metal alloy that includes
silicon, a ceramic, or a CMC. In examples in which substrate 12
includes a ceramic, the ceramic may be substantially homogeneous.
In some examples, a substrate 12 that includes a ceramic includes,
for example, a Si-containing ceramic, such SiO.sub.2, silicon
carbide (SiC) or silicon nitride (Si.sub.3N.sub.4);
Al.sub.2O.sub.3; aluminosilicate (e.g., Al.sub.2SiO.sub.5); or the
like. In other examples, substrate 12 includes a metal alloy that
includes Si, such as a molybdenum-silicon alloy (e.g., MoSi.sub.2)
or a niobium-silicon alloy (e.g., NbSi.sub.2).
[0024] In examples in which substrate 12 includes a CMC, substrate
12 includes a matrix material and a reinforcement material. The
matrix material includes a ceramic material, such as, for example,
SiC, Si.sub.3N.sub.4, Al.sub.2O.sub.3, aluminosilicate, SiO.sub.2,
or the like. The CMC further includes a continuous or discontinuous
reinforcement material. For example, the reinforcement material may
include discontinuous whiskers, platelets, or particulates. As
other examples, the reinforcement material may include a continuous
monofilament or multifilament weave.
[0025] The composition, shape, size, and the like of the
reinforcement material may be selected to provide the desired
properties to the substrate 12 including the CMC. In some examples,
the reinforcement material is chosen to increase the toughness of a
brittle matrix material. The reinforcement material may
additionally or alternatively be chosen to modify a thermal
conductivity, electrical conductivity, thermal expansion
coefficient, hardness, or the like of a substrate 12 including a
CMC.
[0026] In some examples, the composition of the reinforcement
material is the same as the composition of the matrix material. For
example, a matrix material comprising SiC may surround a
reinforcement material comprising SiC whiskers. In other examples,
the reinforcement material includes a different composition than
the composition of the matrix material, such as aluminosilicate
fibers in an Al.sub.2O.sub.3 matrix, or the like. One composition
of a substrate 12 that comprises a CMC includes a reinforcement
material comprising SiC continuous fibers embedded in a matrix
material comprising SiC.
[0027] Some example CMCs used for substrate 12 include composites
of SiC or Si.sub.3N.sub.4 and silicon oxynitride (Si.sub.2N.sub.2O)
or silicon aluminum oxynitride, and oxide-oxide ceramics, such as a
matrix material of Al.sub.2O.sub.3 or aluminosilicate and a
reinforcement material comprising NEXTEL.TM. Ceramic Oxide Fiber
720 (available from 3M Co., St. Paul, Minn.).
[0028] Bond layer 14 is formed directly on substrate 12, and
includes a composition that provides adherence between substrate 12
and a layer formed on bond layer 14, such as EBC 16. In some
examples, the adherence provided by bond layer 14 between substrate
12 and EBC 16 may be greater than the adherence between substrate
12 and EBC 16, without bond layer 14.
[0029] As described above, bond layer 14 may include a composition
that may be stable at temperatures above 1350.degree. C. and/or
above about 1410.degree. C. In this way, bond layer 14 may allow
use of article 10 at temperatures which lead to temperatures of
bond layer 14 above 1350.degree. C. and/or above about 1410.degree.
C. In some examples, article 10 may be used in a environment in
which ambient temperature is greater than the temperature at which
bond layer 14 is stable, e.g., because bond layer 14 may be coated
with at least one layer, such as EBC 16 and/or TBC 22 (FIG. 2),
that provides thermal insulation to bond layer 14 and reduces the
temperature experienced by bond layer 14 compared to the ambient
temperature or the surface temperature of the layer(s) formed on
bond layer 14, e.g., EBC 16.
[0030] In some examples, bond layer 14 may include or consist
essentially of a substantially homogeneous mixture of Si and at
least one of SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2, a rare earth
oxide, ZrSiO.sub.4, TiO.sub.2, Ta.sub.2O.sub.5, B.sub.2O.sub.3, an
alkali metal oxide, or an alkali earth metal oxide. As used herein,
the term "substantially homogenous mixture" includes a mixture that
consists of substantially a single phase, i.e., discrete phases of
distinct composition are substantially not present in the mixture
or in a layer formed by the mixture. For example, a layer including
a substantially homogenous mixture may include a second phase that
is present in an amount of less than 1 volume percent (vol. %).
Also, as used herein, "consist essentially of" means that the
composition includes the listed components, may include additional
components that do not materially affect the basic properties of
the composition, and may not include additional components that
materially affect the basic properties of the composition.
[0031] In some examples, the presence of Si in bond layer 14 may
promote adherence between bond layer 14 and substrate 12, such as,
for example, when substrate 12 includes Si or a compound containing
Si. The addition of an oxide or silicate to bond layer 14 may
contribute to bond layer 14 being stable at temperatures above
1350.degree. C. and/or about 1410.degree. C.
[0032] In some examples, bond layer 14 may include or consist
essentially of up to 99 weight percent (wt. %) Si and a balance of
the at least one of SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2, a rare
earth oxide, ZrSiO.sub.4, TiO.sub.2, Ta.sub.2O.sub.5,
B.sub.2O.sub.3, an alkali metal oxide, or an alkali earth metal
oxide, with a total of 100 wt. %. In other examples, bond layer 14
may include or consist essentially of up to about 50 wt. % Si and a
balance of the at least one of SiO.sub.2, Al.sub.2O.sub.3,
ZrO.sub.2, a rare earth oxide, ZrSiO.sub.4, TiO.sub.2,
Ta.sub.2O.sub.5, B.sub.2O.sub.3, an alkali metal oxide, or an
alkali earth metal oxide, with a total of 100 wt. %.
[0033] In some implementations, bond layer 14 may include or
consist essentially of a substantially homogenous mixture of
silicon, at least one of SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2, or
a rare earth oxide, and at least one of ZrSiO.sub.4, TiO.sub.2,
Ta.sub.2O.sub.5, B.sub.2O.sub.3, an alkali metal oxide, or an
alkali earth metal oxide. In some such examples, bond layer 14 may
include or consist essentially of up to about 99 wt. % Si, up to
about 99 wt. % of the at least one of SiO.sub.2, Al.sub.2O.sub.3,
ZrO.sub.2, or a rare earth oxide, and up to about 50 wt. % of the
at least one of ZrSiO.sub.4, TiO.sub.2, Ta.sub.2O.sub.5,
B.sub.2O.sub.3, an alkali metal oxide, or an alkali earth metal
oxide, with a total of 100 wt. %. In other examples, bond layer 14
may include or consist essentially of up to about 50 wt. % Si, up
to about 99 wt. % of the at least one of SiO.sub.2,
Al.sub.2O.sub.3, ZrO.sub.2, or a rare earth oxide, and up to about
20 wt. % of the at least one of ZrSiO.sub.4, TiO.sub.2,
Ta.sub.2O.sub.5, B.sub.2O.sub.3, an alkali metal oxide, or an
alkali earth metal oxide, with a total of 100 wt. %.
[0034] In other examples, bond layer 14 may include or consist
essentially of Si, an alkali metal oxide, and at least one of
SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2, HfO.sub.2, a rare earth
oxide, ZrSiO.sub.4, HfSiO.sub.4, TiO.sub.2, Ta.sub.2O.sub.5,
B.sub.2O.sub.3, or an alkali earth metal oxide. In some examples in
which bond layer 14 includes or consists essentially of such a
composition, bond layer 14 may include or consist essentially of a
substantially homogeneous mixture. In other examples in which bond
layer 14 includes or consists essentially of such a composition,
bond layer 14 may include two or more discrete phases, e.g., a Si
phase and an oxide phase.
[0035] In some implementations in which bond layer 14 includes or
consists essentially of Si, an alkali metal oxide, and at least one
of SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2, HfO.sub.2, a rare earth
oxide, ZrSiO.sub.4, HfSiO.sub.4, TiO.sub.2, Ta.sub.2O.sub.5,
B.sub.2O.sub.3, or an alkali earth metal oxide, bond layer 14 may
include or consist essentially of up to about 99 wt. % Si, up to
about 50 wt. % of the alkali metal oxide, and up to about 99 wt. %
of the at least one of SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2,
HfO.sub.2, a rare earth oxide, ZrSiO.sub.4, HfSiO.sub.4, TiO.sub.2,
Ta.sub.2O.sub.5, B.sub.2O.sub.3, or an alkali earth metal oxide,
with a total of 100 wt. %. In other implementations, bond layer 14
may include or consist essentially of up to about 50 wt. % Si, up
to about 20 wt. % of the alkali metal oxide, and up to about 99 wt.
% of the at least one of SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2,
HfO.sub.2, a rare earth oxide, ZrSiO.sub.4, HfSiO.sub.4, TiO.sub.2,
Ta.sub.2O.sub.5, B.sub.2O.sub.3, or an alkali earth metal oxide,
with a total of 100 wt. %.
[0036] In some examples, bond layer 14 may include or consist
essentially of Si, an alkali metal oxide, at least one of
SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2, HfO.sub.2, or a rare earth
oxide, and at least one of ZrSiO.sub.4, HfSiO.sub.4, TiO.sub.2,
Ta.sub.2O.sub.5, B.sub.2O.sub.3, or an alkali earth metal oxide. In
some implementations, bond layer 14 may include or consist
essentially of up to about 99 wt. % Si, up to about 50 wt. % of the
alkali metal oxide, and up to about 99 wt. % of the at least one of
SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2, HfO.sub.2, or a rare earth
oxide, and up to about 50 wt. % of the at least one of ZrSiO.sub.4,
HfSiO.sub.4, TiO.sub.2, Ta.sub.2O.sub.5, B.sub.2O.sub.3, or an
alkali earth metal oxide, with a total of 100 wt. %. In other
implementations, bond layer 14 may include or consist essentially
of up to about 50 wt. % Si, up to about 20 wt. % of the alkali
metal oxide, and up to about 99 wt. % of the at least one of
SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2, HfO.sub.2, or a rare earth
oxide, and up to about 20 wt. % of the at least one of ZrSiO.sub.4,
HfSiO.sub.4, TiO.sub.2, Ta.sub.2O.sub.5, B.sub.2O.sub.3, or an
alkali earth metal oxide, with a total of 100 wt. %.
[0037] In other examples, bond layer 14 may include or consist
essentially of B.sub.2O.sub.3. In some examples, in addition to
B.sub.2O.sub.3, bond layer 14 may include or consist essentially of
at least one of Si, SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2,
HfO.sub.2, a rare earth oxide, ZrSiO.sub.4, HfSiO.sub.4, TiO.sub.2,
Ta.sub.2O.sub.5, an alkali metal oxide, or an alkali earth metal
oxide. In some examples, bond layer 14 may include or consist
essentially of up to about 50 wt. % B.sub.2O.sub.3 and a balance of
the at least one of Si, SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2,
HfO.sub.2, a rare earth oxide, ZrSiO.sub.4, HfSiO.sub.4, TiO.sub.2,
Ta.sub.2O.sub.5, an alkali metal oxide, or an alkali earth metal
oxide, with a total of 100 wt. %. In other examples, bond layer 14
may include or consist essentially of up to about 20 wt. %
B.sub.2O.sub.3 and a balance of the at least one of Si, SiO.sub.2,
Al.sub.2O.sub.3, ZrO.sub.2, HfO.sub.2, a rare earth oxide,
ZrSiO.sub.4, HfSiO.sub.4, TiO.sub.2, Ta.sub.2O.sub.5, an alkali
metal oxide, or an alkali earth metal oxide, with a total of 100
wt. %.
[0038] In some examples, bond layer 14 may include or consist
essentially of B.sub.2O.sub.3, Si, at least one of SiO.sub.2,
Al.sub.2O.sub.3, ZrO.sub.2, HfO.sub.2, or a rare earth oxide, and
at least one of ZrSiO.sub.4, HfSiO.sub.4, TiO.sub.2,
Ta.sub.2O.sub.5, an alkali metal oxide, or an alkali earth metal
oxide. In some implementations, bond layer 14 may include or
consist essentially of up to about 50 wt. % B.sub.2O.sub.3, up to
about 99 wt. % Si, up to about 99 wt. % of the at least one of
SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2, HfO.sub.2, or a rare earth
oxide, and up to about 50 wt. % of the at least one of ZrSiO.sub.4,
HfSiO.sub.4, TiO.sub.2, Ta.sub.2O.sub.5, an alkali metal oxide, or
an alkali earth metal oxide, with a total of 100 wt. %. In other
implementations, bond layer 14 may include or consist essentially
of up to about 20 wt. % B.sub.2O.sub.3, up to about 50 wt. % Si, up
to about 99 wt. % of the at least one of SiO.sub.2,
Al.sub.2O.sub.3, ZrO.sub.2, HfO.sub.2, or a rare earth oxide, and
up to about 20 wt. % of the at least one of ZrSiO.sub.4,
HfSiO.sub.4, TiO.sub.2, Ta.sub.2O.sub.5, an alkali metal oxide, or
an alkali earth metal oxide, with a total of 100 wt. %.
[0039] Regardless of the composition of bond layer 14, bond layer
14 may have a thickness of less than about 200 micrometers (.mu.m;
about 0.007874 inch). In some examples, bond layer 14 may include a
thickness of up to about 50 .mu.m (about 0.001969 inch), up to
about 25 .mu.m (about 0.0009843 inch), or between about 1 .mu.m
(about 0.00003937 inch) and about 25 .mu.m (about 0.0009843 inch).
In some examples, a bond layer 14 may be thinner when bond layer 14
includes a greater amount of Si and thicker when bond layer 14
includes a lesser amount of Si.
[0040] Bond layer 14 may be formed on substrate 12 using, for
example, plasma spraying, physical vapor deposition (PVD), electron
beam physical vapor deposition (EB-PVD), directed vapor deposition
(DVD), chemical vapor deposition (CVD), cathodic arc deposition
slurry process deposition, sol-gel process deposition, or
electrophoretic deposition.
[0041] In some examples in which bond layer 14 includes at least
two components (e.g., Si and at least one other component), the at
least two components may be co-deposited. Alternatively, in
examples in which bond layer 14 includes at least two components,
at least one of the at least two components may be deposited in a
separate layer from at least one other of the at least two
components. For example, when bond layer 14 includes Si and at
least one oxide or ZrSiO.sub.4 (referred to hereafter as oxide for
brevity), Si may be deposited in a separate layer from the oxide.
As examples, Si and oxide may be deposited on substrate 12 in the
following orders: Si/O; O/Si; Si/O/Si/O; O/Si/O/Si. Of course, the
deposition process is not limited to two or fewer Si layers and/or
two or fewer oxide layers, and as many alternating layers of Si and
oxide may be deposited as desired.
[0042] In some examples in which bond layer 14 includes at least
two oxides (and/or ZrSiO.sub.4), at least one of the at least two
oxides may be deposited in a separate layer from at least one other
of the at least two oxides. In some implementations, at least one
of the at least two oxides may be co-deposited with Si, while at
least one other oxide may be deposited in a separate layer. In
other implementations, Si, at least one of the at least two oxides,
and at least another of the at least two oxides may be deposited in
three or more separate layers. To summarize, the components of bond
layer 14 may be deposited in any combination of separately
deposited layers and/or co-deposited layers.
[0043] As described above, in some examples, bond layer 14 may
include or consist essentially of a substantially homogenous
mixture. In some examples, bond layer 14 is deposited as a
substantially homogeneous layer, e.g., when bond layer 14 includes
at least two components, the at least two components may be
co-deposited as a substantially homogenous layer. In other
examples, such as when bond layer 14 is deposited as multiple
layers having different compositions, bond layer 14 may undergo a
post-deposition heat treatment to form the substantially homogenous
layer.
[0044] For example bond layer 14 may be exposed to a
post-deposition heat treatment at a temperature up to the
temperature capability of substrate 12, which may be, for example,
up to about 1500.degree. C. for some substrates 12 that include a
CMC. In some examples, the post-deposition heat treatment
temperature may be between about 1350.degree. C. and about the
temperature capability of substrate 12 (e.g., about 1500.degree.
C.). Bond layer 14 may be exposed to the heat treatment for up to
about 10 hours, such as between about 10 minutes and about 1 hour.
The heat treatment may be performed in an oxidizing atmosphere,
such as air; a reducing atmosphere, such as hydrogen; or an inert
atmosphere, such as argon, helium, or nitrogen. In some examples,
bond layer 14 may undergo the heat treatment after deposition of
bond layer 14 on substrate 12 and before deposition of an overlayer
such as EBC 16. In other examples, bond layer 14 may undergo the
heat treatment after deposition of bond layer 14 on substrate 12
and after deposition of an overlayer such as EBC 16.
[0045] While the post-deposition heat treatment may in some
implementations be used to create a substantially homogenous
mixture in bond layer 14, post-deposition heat treatment may also
cause chemical reactions among components of bond layer 14 and/or
between components of bond layer 14 and components of substrate 12
and/or between components of bond layer 14 and components of an
overlayer, such as EBC 16. This may contribute to adherence between
substrate 12 and bond layer 14 and/or between bond layer 14 and an
overlayer, such as EBC 16. Accordingly, bond layer 14 may or may
not undergo heat treatment in examples in which bond layer 14 does
not include a substantially homogenous mixture and/or in examples
in which bond layer 14 is deposited as a substantially homogenous
mixture. Hence, regardless of the composition, phase constitution,
and/or deposition process used to form bond layer 14, layer 14 may
or may not be exposed to a post-deposition heat treatment.
[0046] EBC 16 is formed on bond layer 14. EBC 16 may reduce or
substantially prevent attack of bond layer 14 and/or substrate 12
by chemical species present in the environment in which article 10
is utilized, e.g., in the intake gas or exhaust gas of a gas
turbine engine. For example, EBC 16 may include a material that is
resistant to oxidation or water vapor attack. Exemplary materials
for use in EBC 16 include mullite; glass ceramics such as barium
strontium aluminosilicate (BaO--SrO--Al.sub.2O.sub.3-2SiO.sub.2;
BSAS), calcium aluminosilicate (CaAl.sub.2Si.sub.2O.sub.8; CAS),
cordierite (magnesium aluminosilicate), and lithium
aluminosilicate; and rare earth silicates (silicates of Lu, Yb, Tm,
Er, Ho, Dy, Tb, Gd, Eu, Sm, Pm, Nd, Pr, Ce, La, Y, or Sc). The rare
earth silicate may be a rare earth mono-silicate
(RE.sub.2SiO.sub.5, where RE stands for "rare earth") or a rare
earth di-silicate (RE.sub.2Si.sub.2O.sub.7, where RE stands for
"rare earth"). In some examples, EBC 16 is formed as a
substantially non-porous layer, while in other examples, EBC 16 is
formed as a layer that includes a plurality of cracks. EBC 16 may
be formed using, for example, CVD; PVD, including EB-PVD and DVD;
plasma spraying or another thermal spraying process, or the like.
In some examples, EBC 16 may comprise a thickness between about
0.001 inch and about 0.1 inch. EBC 16 may be formed on bond layer
14 prior to exposing bond layer 14 to a heat treatment or after
exposing bond layer 14 to a heat treatment, as described above. In
some examples, EBC 16 may comprise a thickness between about 0.003
inch (about 76.2 .mu.m) and about 0.05 inch (about 1270 .mu.m).
[0047] In some examples, an article may include a layer other than
EBC 16 formed on bond layer 14. FIG. 2 is a conceptual
cross-sectional diagram that illustrates an example of an article
20 that includes bond layer 14 formed on substrate 12 and a TBC 22
formed on bond layer 14. TBC 22 includes a thermally insulative
material. Common TBCs include ceramic layers comprising ZrO.sub.2
or HfO.sub.2. A TBC 22 that includes ZrO.sub.2 or HfO.sub.2
optionally may include one or more other elements or compounds to
modify a desired characteristic of the TBC 22, such as, for
example, phase stability, thermal conductivity, or the like.
Exemplary additive elements or compounds include rare earth oxides
(oxides of Lu, Yb, Tm, Er, Ho, Dy, Tb, Gd, Eu, Sm, Pm, Nd, Pr, Ce,
La, Y, or Sc). Particular examples of materials from which TBC 22
may be formed include ZrO.sub.2 stabilized with between 7 weight
percent (wt. %) and 8 wt. % Y.sub.2O.sub.3; ZrO.sub.2 stabilized
with Yb.sub.2O.sub.3, Sm.sub.2O.sub.3, and at least one of
Lu.sub.2O.sub.3, Sc.sub.2O.sub.3, Ce.sub.2O.sub.3, Gd.sub.2O.sub.3,
Nd.sub.2O.sub.3, or Eu.sub.2O.sub.3; or HfO.sub.2 stabilized with
Yb.sub.2O.sub.3, Sm.sub.2O.sub.3, and at least one of
Lu.sub.2O.sub.3, Sc.sub.2O.sub.3, Ce.sub.2O.sub.3, Gd.sub.2O.sub.3,
Nd.sub.2O.sub.3, or Eu.sub.2O.sub.3. In some examples, TBC 22 may
include ZrO.sub.2 and/or HfO.sub.2 in combination with additive
elements or compounds such that at least some of the stabilized
ZrO.sub.2 and/or HfO.sub.2 forms a metastable tetragonal-prime
crystalline phase, a cubic crystalline phase, or a compound phase
(RE.sub.2Zr.sub.2O.sub.7 or RE.sub.2Hf.sub.2O.sub.7, where RE is a
rare earth element).
[0048] In some examples, TBC 22 includes ZrO.sub.2 and/or
HfO.sub.2, a primary dopant, a first co-dopant, and a second
co-dopant. The primary dopant is preferably present in a greater
amount than either the first or second co-dopants, and may be
present in an amount less than, equal to, or greater than the total
amount of the first and second co-dopants. The primary dopant
includes Yb.sub.2O.sub.3, the first co-dopant includes
Sm.sub.2O.sub.3, and the second co-dopant includes at least one of
Lu.sub.2O.sub.3, Sc.sub.2O.sub.3, Ce.sub.2O.sub.3, Gd.sub.2O.sub.3,
Nd.sub.2O.sub.3, or Eu.sub.2O.sub.3.
[0049] In some examples, TBC 22 includes between about 2 mol. % and
about 40 mol. % of the primary dopant. In other examples, TBC 22
includes between approximately 2 mol. % and approximately 20 mol. %
of the primary dopant or between approximately 2 mol. % and
approximately 10 mol. % of the primary dopant.
[0050] In some examples, TBC 22 includes between about 0.1 mol. %
and about 20 mol. % of the first co-dopant. In other examples, TBC
22 includes between about 0.5 mol. % and about 10 mol. % of the
first co-dopant or between about 0.5 mol. % and about 5 mol. % of
the first co-dopant.
[0051] In some examples, TBC 22 includes between about 0.1 mol. %
and about 20 mol. % of the second co-dopant. In other examples, TBC
22 includes between about 0.5 mol. % and about 10 mol. % of the
second co-dopant or between about 0.5 mol. % and about 5 mol. % of
the second co-dopant.
[0052] In some examples, the composition of TBC 22 provides a
desired phase constitution. For a first barrier coating layer 18
including ZrO.sub.2 and/or HfO.sub.2, a primary dopant, a first
co-dopant, and a second co-dopant, accessible phase constitutions
include metastable tetragonal-prime, cubic, and compound
(RE.sub.2Zr.sub.2O.sub.7 and RE.sub.2Hf.sub.2O.sub.7, where RE is a
rare earth element). To achieve a RE.sub.2O.sub.3--ZrO.sub.2
(and/or HfO.sub.2) compound phase constitution, TBC 22 includes
between about 20 mol. % and about 40 mol. % primary dopant, between
about 10 mol. % and about 20 mol. % first co-dopant, between about
10 mol. % and about 20 mol. % second co-dopant, and the balance
base oxide (ZrO.sub.2 and/or HfO.sub.2) and any impurities present.
To achieve a cubic phase constitution, TBC 22 includes between
about 5 mol. % and about 20 mol. % primary dopant, between about 2
mol. % and about 10 mol. % first co-dopant, between about 2 mol. %
and about 10 mol. % second co-dopant, and a balance base oxide
(ZrO.sub.2 and/or HfO.sub.2) and any impurities present. In some
examples, to achieve a metastable tetragonal phase constitution,
TBC 22 includes between about 2 mol. % and about 5 mol. % primary
dopant, between about 0.5 mol. % and about 3 mol. % first
co-dopant, between about 0.5 mol. % and about 3 mol. % second
co-dopant, and a balance base oxide and any impurities present.
[0053] TBC 22 may be formed on bond layer 14 as a porous layer or a
columnar layer, and may be formed using, for example, CVD; PVD,
including EB-PVD and DVD; plasma spraying or another thermal
spraying process, or the like.
[0054] In some examples, an article may include a layer other than
EBC 16 or TBC 22 formed on bond layer 14. FIG. 3 is a conceptual
cross-sectional diagram that illustrates an example of an article
30 that includes bond layer 14 formed on substrate 12 and a
CMAS-resistant layer 32 formed on bond layer 14. CMAS-resistant
layer 32 includes an element or compound that reacts with CMAS to
form a solid or a highly-viscous reaction product (i.e., a reaction
product that is a solid or highly viscous at the temperatures
experienced by article 30). In some examples, CMAS-resistant layer
32 includes Al.sub.2O.sub.3 and at least one rare earth oxide, such
as, for example, an oxide of at least one of Sc, Y, La, Ce, Pr, Nd,
Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and combinations
thereof. The combination of Al.sub.2O.sub.3 and at least one rare
earth oxide may allow tailoring of one or more properties of
CMAS-resistant layer 32, such as, for example, the chemical
reactivity of CMAS-resistant layer 32 with CMAS, the viscosity of
the reaction products, the coefficient of thermal expansion (CTE)
of CMAS-resistant layer 32, the chemical compatibility of
CMAS-resistant layer 32 with bond layer 14, or the like.
[0055] In some examples, CMAS-resistant layer 32 is essentially
free of ZrO.sub.2 and/or HfO.sub.2. That is, in these examples,
CMAS-resistant layer 32 includes at most trace amounts of ZrO.sub.2
and/or HfO.sub.2, such as, for example, the amounts present in
commercially-available rare earth oxides.
[0056] In some examples, CMAS-resistant layer 32 includes SiO.sub.2
in addition to the Al.sub.2O.sub.3 and at least one rare earth
oxide. SiO.sub.2 can be added to CMAS-resistant layer 32 to allow
further manipulation of the properties of CMAS-resistant layer 32,
such as, for example, the chemical reactivity, viscosity of the
reaction products, the CTE, the chemical compatibility of
CMAS-resistant layer 32 with bond layer 14, or the like.
[0057] In some examples, CMAS-resistant layer 32 optionally
includes other additive components, such as, for example,
TiO.sub.2, Ta.sub.2O.sub.5, HfSiO.sub.4, alkali metal oxides,
alkali earth metal oxides, or mixtures thereof. The additive
components may be added to CMAS-resistant layer 32 to modify one or
more desired properties of CMAS-resistant layer 32. For example,
the additive components may increase or decrease the reaction rate
of CMAS-resistant layer 32 with CMAS, may modify the viscosity of
the reaction product from the reaction of CMAS and CMAS-resistant
layer 32, may increase adhesion of the CMAS-resistant layer 32 to
bond layer 14, may increase or decrease the chemical stability of
CMAS-resistant layer 32, or the like.
[0058] CMAS-resistant layer 32 may include up to about 99 mol. % of
the at least one rare earth oxide, .+-.1 mol. %, and up to about 90
mol. % of Al.sub.2O.sub.3, with a total of 100 mol. %. In some
examples, CMAS-resistant layer 32 may also include up to about 90
mol. % of SiO.sub.2. In some examples, CMAS-resistant layer 32 may
additionally include up to about 50 mol. % of at least one of
TiO.sub.2, Ta.sub.2O.sub.5, HfSiO.sub.4, an alkali oxide, or an
alkali earth oxide.
[0059] In some examples, CMAS-resistant layer 32 includes between
about 20 mol. % and about 80 mol. % of at least one rare earth
oxide, between about 5 mol. % and about 50 mol. % Al.sub.2O.sub.3,
and, optionally, between about 5 mol. % to about 50 mol. % of
SiO.sub.2. In some examples, CMAS-resistant layer 32 may
additionally include between about 0.1 mol. % and about 30 mol. %
of at least one of TiO.sub.2, Ta.sub.2O.sub.5, HfSiO.sub.4, an
alkali oxide, or an alkali earth oxide.
[0060] As described above, CMAS-resistant layer 32 reacts with CMAS
that reaches layer 32 to form a solid or highly viscous reaction
product. The reaction product may have a melting temperature
significantly higher than CMAS (e.g., higher than about
1200-1250.degree. C.). A solid or highly viscous reaction product
is desired because the CMAS-resistant layer 32 is consumed as it
reacts with CMAS. If, for example, the reaction product of
CMAS-resistant layer 32 and CMAS was a relatively low viscosity
liquid, the low viscosity liquid would contact bond layer 14 and/or
substrate 12 once the CMAS-resistant layer 32 is consumed by the
reaction, which is the very occurrence the CMAS-resistant layer 32
is designed to prevent.
[0061] If the reaction product is a solid or highly viscous,
however, a reaction layer will form on the surface of
CMAS-resistant layer 32, which will lower the reaction rate of the
CMAS with CMAS-resistant layer 32. That is, once a solid or highly
viscous reaction layer forms on the surface of CMAS-resistant layer
32, the reaction between CMAS-resistant layer 32 and CMAS will
slow, because any further reaction will require the diffusion of
CMAS through the reaction layer to encounter the CMAS-resistant
layer 32, or diffusion of a component of CMAS-resistant layer 32
through the reaction layer to encounter the CMAS. In either case,
the diffusion of either CMAS or the component of CMAS-resistant
layer 32 is expected to be the limiting step in the reaction once a
solid or highly viscous reaction layer is formed on the surface of
CMAS-resistant layer 32, because diffusion will be the slowest
process.
[0062] Although EBC 16, TBC 22, and CMAS-resistant layer 32 have
been described is separate examples as being formed on bond layer
14, in some examples, at least two of EBC 16, TBC 22, and
CMAS-resistant layer 32 may be formed over bond layer 14. FIG. 4 is
a conceptual cross-sectional diagram that illustrates an example of
an article 40 that includes bond layer 14 formed on substrate 12,
EBC 16 formed on bond layer 14, TBC 22 formed on EBC 16, and
CMAS-resistant layer 32 formed on TBC 22. As used herein, "formed
over" means a layer or coating that is formed on top of another
layer or coating, and encompasses both a first layer or coating
formed immediately adjacent a second layer or coating and a first
layer or coating formed on top of a second layer or coating with
one or more intermediate layer or coating present between the first
and second layers or coatings. In contrast, "formed directly on"
and "formed on" denote a layer or coating that is formed
immediately adjacent another layer or coating, i.e., there are no
intermediate layers or coatings.
[0063] Although FIG. 4 illustrates an article 40 that includes EBC
16, TBC 22, and CMAS-resistant layer 32, in other examples, an
article may include two of these layers. For example, an article
may include substrate 12, bond layer 14 formed on substrate 12, EBC
16 formed over bond layer 14, and TBC 22 formed over EBC 16. As
another example, an article may include substrate 12, bond layer 14
formed on substrate 12, TBC 22 formed over bond layer 14, and
CMAS-resistant layer 32 formed over TBC 22.
[0064] Additionally, while CMAS-resistant layer 32 is formed over
TBC 22, which is formed over EBC 16 in FIG. 4, other configurations
of layers are possible. For example, TBC 22 may be formed over
CMAS-resistant layer 32 and/or EBC 16 may be formed over TBC 22.
Other configurations and combinations of layers will be apparent to
those of ordinary skill in the art, and fall within the scope of
the disclosure and the following claims.
EXAMPLES
Example 1
[0065] FIG. 5 is a cross-sectional micrograph of an example article
50 that includes a bond layer formed in accordance with the aspects
of the disclosure. Article 50 includes a substrate 52 that includes
a SiC matrix reinforced with SiC fibers, a bond layer 54 that
includes Si, SiO.sub.2, Yb.sub.2O.sub.3, and ZrO.sub.2, and an EBC
56 that includes Yb.sub.2Si.sub.2O.sub.7 (ytterbium disilicate).
The components of bond layer 54 were co-deposited in a single layer
on substrate 52 using DVD, and EBC 56 was deposited using DVD on
bond layer 54 prior to exposing bond layer 54 to heat treatment.
Article 50 was then exposed to heat treatment in air at about
1410.degree. C. for about 1 hour prior to testing.
[0066] Article 50 was then exposed to 100 hour thermal cycling with
1 hour cycles in 90% H.sub.2O and 10% O.sub.2 atmosphere at about
1430.degree. C. (above the melting temperature of pure silicon).
FIG. 5 illustrates a portion of article 50 after completion of the
thermal cycling testing. FIG. 5 illustrates that EBC 56 maintained
good adherence to bond layer 54 and substrate 52 after the thermal
cycling.
Example 2
[0067] FIG. 6 is a cross-sectional micrograph of an example article
60 that includes a bond layer formed in accordance with the aspects
of the disclosure. Article 60 includes a substrate 62 that includes
a SiC matrix reinforced with SiC fibers, a bond layer 64 that
includes Si, SiO.sub.2, Yb.sub.2O.sub.3, and ZrO.sub.2, and an EBC
66 that includes Yb.sub.2Si.sub.2O.sub.7 (ytterbium disilicate).
The components of bond layer 64 were co-deposited in a single layer
on substrate 62 using DVD, and EBC 66 was deposited using DVD on
bond layer 64 prior to exposing bond layer 64 to heat treatment.
Article 50 was then exposed to heat treatment in air at about
1430.degree. C. for about 1 hour prior to testing.
[0068] Article 60 was then exposed to 100 hour thermal cycling with
1 hour cycles in 90% H.sub.2O and 10% O.sub.2 atmosphere at about
1450.degree. C. (above the melting temperature of pure silicon).
FIG. 6 illustrates a portion article 60 after completion of the
thermal cycling testing. FIG. 6 illustrates that EBC 66 maintained
good adherence to bond layer 64 and substrate 62 after the thermal
cycling.
[0069] Various examples have been described. These and other
examples are within the scope of the following claims.
* * * * *