WO2012129431A1

WO2012129431A1 - Bond layers for ceramic or ceramic matrix composite substrates

Info

Publication number: WO2012129431A1
Application number: PCT/US2012/030174
Authority: WO
Inventors: Kang N. Lee
Original assignee: Rolls-Royce Corporation
Priority date: 2011-03-23
Filing date: 2012-03-22
Publication date: 2012-09-27
Also published as: US20140072816A1; EP2688858A1

Abstract

A bond layer may include a composition that may be stable at temperatures above about 1410° 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 SiO₂, Al₂O₃, ZrO₂, a rare earth oxide, ZrSiO₄, TiO₂, Ta₂O₅, B₂O₃, 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 SiO₂, Al₂O₃, ZrO₂, HfO₂, a rare earth oxide, ZrSiO₄, HfSiO₄, TiO₂, Ta₂O₅, B₂O₃, or an alkali earth metal oxide. In other examples, the bond layer may include B₂O₃.

Description

BOND LAYERS FOR CERAMIC OR CERAMIC MATRIX COMPOSITE

SUBSTRATES

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°C, with short-term peaks as high as 1100 °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°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 (Si0₂), alumina (AI₂O₃), zirconia (Zr0₂), a rare earth oxide (RE₂O₃, 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 (ZrSi0₄), titanium oxide (Ti0₂), tantalum oxide (Ta₂0₅), boron oxide (B₂0₃), an alkali metal oxide (Li₂0, Na₂0, K₂0, Rb₂0, Cs₂0, or Fr₂0), 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 Si0₂, A1₂0₃, Zr0₂, hafnia (Hf0₂), a rare earth oxide, ZrSi0₄, hafnium silicate (HfSi0₄), Ti0₂, Ta₂0₅, B₂0₃, or an alkali earth metal oxide. In other examples, the bond layer may include B₂0₃.

[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 Si0₂, A1₂0₃, Zr0₂, a rare earth oxide, ZrSi0₄, Ti0₂, Ta₂0₅, B₂0₃, 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 Si0₂, A1₂0₃, Zr0₂, Hf0₂, a rare earth oxide, ZrSi0₄, HfSi0₄, Ti0₂, Ta₂0₅, B₂0₃, 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 B₂0₃. The article also may include at least one of a TBC, an EBC, or a CM AS -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 CM AS -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 Si0₂, A1₂0₃, Zr0₂, a rare earth oxide, ZrSi0₄, Ti0₂, Ta₂Os, B₂0₃, 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 Si0₂, A1₂0₃, Zr0₂, Hf0₂, a rare earth oxide, ZrSi0₄, HfSi0₄, Ti0₂, Ta₂0₅, B₂0₃, 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 B₂0₃.

[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°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°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°C or even greater than 1410°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°C (about 2700°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°C or greater than about 1410°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°C or greater than about 1410°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 Si0₂, silicon carbide (SiC) or silicon nitride (Si₃N₄); A1₂0₃; aluminosilicate (e.g., Al₂Si0₅); or the like. In other examples, substrate 12 includes a metal alloy that includes Si, such as a molybdenum-silicon alloy (e.g., MoSi₂) or a niobium-silicon alloy (e.g., NbSi₂).

[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, Si₃N₄, A1₂0₃, aluminosilicate, Si0₂, 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 Α1₂0₃ 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 S1₃N₄ and silicon oxynitride (S1₂N₂O) or silicon aluminum oxynitride, and oxide- oxide ceramics, such as a matrix material of AI₂O₃ or aluminosilicate and a reinforcement material comprising NEXTEL™ Ceramic Oxide Fiber 720

(available from 3M Co., St. Paul, MN).

[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°C and/or above about 1410°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°C and/or above about 1410°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 Si0₂, A1₂0₃, Zr0₂, a rare earth oxide, ZrSi0₄, Ti0₂, Ta₂0₅, B₂0₃, 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°C and/or about 1410°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 Si0₂, A1₂0₃, Zr0₂, a rare earth oxide, ZrSi0₄, Ti0₂, Ta₂0₅, B₂0₃, 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 Si0₂, A1₂0₃, Zr0₂, a rare earth oxide, ZrSi0₄, Ti0₂, Ta₂0₅, B₂0₃, 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 Si0₂, A1₂0₃, Zr0₂, or a rare earth oxide, and at least one of ZrSi0₄, Ti0₂, Ta₂0₅, B₂0₃, 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 Si0₂, A1₂0₃, Zr0₂, or a rare earth oxide, and up to about 50 wt. % of the at least one of ZrSi0₄, Ti0₂, Ta₂0₅, B₂0₃, 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 Si0₂, A1₂0₃, Zr0₂, or a rare earth oxide, and up to about 20 wt. % of the at least one of ZrSi0₄, Ti0₂, Ta₂Os, B₂0₃, 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 Si0₂, A1₂0₃, Zr0₂, Hf0₂, a rare earth oxide, ZrSi0₄, HfSi0₄, Ti0₂, Ta₂Os, B₂0₃, 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 Si0₂, A1₂0₃, Zr0₂, Hf0₂, a rare earth oxide, ZrSi0₄, HfSi0₄, Ti0₂, Ta₂Os, B₂0₃, 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 Si0₂, A1₂0₃, Zr0₂, Hf0₂, a rare earth oxide, ZrSi0₄, HfSi0₄, Ti0₂, Ta₂C"5, B₂0₃, 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 Si0₂, A1₂0₃, Zr0₂, Hf0₂, a rare earth oxide, ZrSi0₄, HfSi0₄, Ti0₂, Ta₂C"5, B₂0₃, 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 Si0₂, A1₂0₃, Zr0₂, Hf0₂, or a rare earth oxide, and at least one of ZrSi0₄, HfSi0₄, Ti0₂, Ta₂0₅, B₂0₃, 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 Si0₂, A1₂0₃, Zr0₂, Hf0₂, or a rare earth oxide, and up to about 50 wt. % of the at least one of ZrSi0₄, HfSi0₄, Ti0₂, Ta₂0₅, B₂O₃, 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 Si0₂, A1₂0₃, Zr0₂, Hf0₂, or a rare earth oxide, and up to about 20 wt. % of the at least one of ZrSi0₄, HfSi0₄, Ti0₂, Ta₂0₅, B₂0₃, 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 B₂0₃. In some examples, in addition to B₂0₃, bond layer 14 may include or consist essentially of at least one of Si, Si0₂, A1₂0₃, Zr0₂, Hf0₂, a rare earth oxide, ZrSi0₄, HfSi0₄, Ti0₂, Ta₂0₅, 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. % B₂0₃ and a balance of the at least one of Si, Si0₂, A1₂0₃, Zr0₂, Hf0₂, a rare earth oxide, ZrSi0₄, HfSi0₄, Ti0₂, Ta₂0₅, 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. % B₂0₃ and a balance of the at least one of Si, Si0₂, A1₂0₃, Zr0₂, Hf0₂, a rare earth oxide, ZrSi0₄, HfSi0₄, Ti0₂, Ta₂0₅, 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 B₂0₃, Si, at least one of Si0₂, A1₂0₃, Zr0₂, Hf0₂, or a rare earth oxide, and at least one of ZrSi0₄, HfSi0₄, Ti0₂, Ta₂Os, 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. % B₂0₃, up to about 99 wt. % Si, up to about 99 wt. % of the at least one of Si0₂, A1₂0₃, Zr0₂, Hf0₂, or a rare earth oxide, and up to about 50 wt. % of the at least one of ZrSi0₄, HfSi0₄, Ti0₂, Ta₂Os, 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. % B₂0₃, up to about 50 wt. % Si, up to about 99 wt. % of the at least one of Si0₂, A1₂0₃, Zr0₂, Hf0₂, or a rare earth oxide, and up to about 20 wt. % of the at least one of ZrSi0₄, HfSi0₄, Ti0₂, Ta₂0₅, 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 (μιη; about 0.007874 inch). In some examples, bond layer 14 may include a thickness of up to about 50 μιη (about 0.001969 inch), up to about 25 μιη (about 0.0009843 inch), or between about 1 μιη (about 0.00003937 inch) and about 25 μιη (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 ZrSi0₄ (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 ZrSi0₄), 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°C for some substrates 12 that include a CMC. In some examples, the post-deposition heat treatment temperature may be between about 1350°C and about the temperature capability of substrate 12 (e.g., about 1500°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 overlay er 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 overlay er 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 overlay er, such as EBC 16. This may contribute to adherence between substrate 12 and bond layer 14 and/or between bond layer 14 and an overlay er, 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-Al₂03-2Si02; BSAS), calcium aluminosilicate (CaAl₂Si₂08; 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 (RE₂Si0₅, where RE stands for "rare earth") or a rare earth di-silicate (RE₂S1₂O₇, 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 μιη) and about 0.05 inch (about 1270 μπι).

[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 Zr0₂ or Hf0₂. A TBC 22 that includes Zr0₂ or Hf0₂ 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 Zr0₂ stabilized with between 7 weight percent (wt. %) and 8 wt. % Y₂0₃; Zr0₂ stabilized with Yb₂0₃, Sm₂0₃, and at least one of Lu₂0₃, Sc₂0₃, Ce₂0₃, Gd₂0₃, Nd₂0₃, or Eu₂0₃; or Hf0₂ stabilized with Yb₂0₃, Sm₂0₃, and at least one of Lu₂0₃, Sc₂0₃, Ce₂0₃, Gd₂0₃, Nd₂0₃, or Eu₂0₃. In some examples, TBC 22 may include Zr0₂ and/or Hf0₂ in combination with additive elements or compounds such that at least some of the stabilized Zr0₂ and/or Hf0₂ forms a metastable tetragonal-prime crystalline phase, a cubic crystalline phase, or a compound phase (RE₂Zr₂0₇ or RE₂Hf₂0₇, where RE is a rare earth element).

[0048] In some examples, TBC 22 includes Zr0₂ and/or Hf0₂, 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 Yb₂0₃, the first co-dopant includes Sm₂0₃, and the second co-dopant includes at least one of Lu₂0₃, Sc₂0₃, Ce₂0₃, Gd₂0₃, Nd₂0₃, or Eu₂0₃.

[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 Zr0₂ and/or Hf0₂, a primary dopant, a first co-dopant, and a second co-dopant, accessible phase constitutions include metastable tetragonal-prime, cubic, and compound (RE₂Zr₂0₇ and RE₂Hf₂0₇, where RE is a rare earth element). To achieve a RE₂03-Zr0₂ (and/or Hf0₂) 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 (Zr0₂ and/or Hf0₂) 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 (Zr0₂ and/or Hf0₂) 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 A1₂0₃ 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 A1₂0₃ 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 Zr0₂ and/or Hf0₂. That is, in these examples, CMAS-resistant layer 32 includes at most trace amounts of Zr0₂ and/or Hf0₂, such as, for example, the amounts present in commercially-available rare earth oxides.

[0056] In some examples, CMAS-resistant layer 32 includes Si0₂ in addition to the A1₂0₃ and at least one rare earth oxide. Si0₂ 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, Ti0₂, Ta₂0₅, HfSi0₄, 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 A1₂0₃, with a total of 100 mol. %. In some examples, CMAS-resistant layer 32 may also include up to about 90 mol. % of Si0₂. In some examples, CMAS-resistant layer 32 may additionally include up to about 50 mol. % of at least one of Ti0₂, Ta₂0₅, HfSi0₄, 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. % A1₂0₃, and, optionally, between about 5 mol. % to about 50 mol. % of Si0₂. In some examples, CMAS-resistant layer 32 may additionally include between about 0.1 mol. % and about 30 mol. % of at least one of Ti0₂, Ta₂0₅, HfSi0₄, 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°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, Si0₂, Yb₂0₃, and Zr0₂, and an EBC 56 that includes Yb₂Si₂0₇ (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°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% H₂0 and 10% 0₂ atmosphere at about 1430°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, Si0₂, Yb₂0₃, and Zr0₂, and an EBC 66 that includes Yb₂Si₂0₇ (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°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% H₂0 and 10% 0₂ atmosphere at about 1450°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.

Claims

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 Si0₂, A1₂0₃, Zr0₂, a rare earth oxide, ZrSi0₄, Ti0₂, Ta₂Os, B₂0₃, 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 CM AS -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 Si0₂, A1₂0₃, Zr0₂, a rare earth oxide, ZrSi0₄, Ti0₂, Ta₂0₅, B₂0₃, an alkali metal oxide, or an alkali earth metal oxide.

3. The article of claim 3, wherein the bond layer comprises up to about 50 wt. % Si and a balance of the at least one of Si0₂, A1₂0₃, Zr0₂, a rare earth oxide, ZrSi0₄, Ti0₂, Ta₂0₅, B₂0₃, an alkali metal oxide, or an alkali earth metal oxide, with a total of 100 wt. %.

4. The article of claim 1, wherein the bond layer comprises a substantially homogeneous mixture of Si; at least one of Si0₂, A1₂0₃, Zr0₂, or a rare earth oxide; and at least one of ZrSi0₄, Ti0₂, Ta₂0₅, B₂0₃, an alkali metal oxide, or an alkali earth metal oxide.

5. The article of claim 4, wherein the bond layer consists essentially of a substantially homogeneous mixture of Si; at least one of Si0₂, A1₂0₃, Zr0₂, or a rare earth oxide; and at least one of ZrSi0₄, Ti0₂, Ta₂0₅, B₂0₃, an alkali metal oxide, or an alkali earth metal oxide.

6. The article of claim 7, wherein the bond layer comprises up to about 50 wt. % Si, up to about 99 wt. % of the at least one of Si0₂, A1₂0₃, Zr0₂, or a rare earth oxide, and up to about 20 wt. % of the at least one of ZrSi0₄, Ti0₂, Ta₂0₅, B₂0₃, an alkali metal oxide, or an alkali earth metal oxide, with a total of 100 wt. %.

7. The article of claim 7, wherein the bond layer has a thickness of less than about 50 μιη.

8. An article comprising:

a bond layer formed on the substrate, wherein the bond layer comprises Si; an alkali metal oxide; and at least one of Si0₂, A1₂0₃, Zr0₂, Hf0₂, a rare earth oxide, ZrSi0₄, HfSi0₄, Ti0₂, Ta₂0₅, B₂0₃, 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 CM AS -resistant layer.

9. The article of claim 8, wherein consists essentially of Si; the alkali metal oxide; and the at least one of Si0₂, A1₂0₃, Zr0₂, Hf0₂, a rare earth oxide, ZrSi0₄, HfSi0₄, Ti0₂, Ta₂0₅, B₂0₃, or an alkali earth metal oxide.

10. The article of claim 8 or 9, wherein the bond layer consists essentially of a substantially homogeneous mixture of Si; the alkali metal oxide; and the at least one of Si0₂, A1₂0₃, Zr0₂, Hf0₂, a rare earth oxide, ZrSi0₄, HfSi0₄, Ti0₂, Ta₂0₅, B₂0₃, or an alkali earth metal oxide.

11. The article of claim 10, 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 Si0₂, A1₂0₃, Zr0₂, Hf0₂, a rare earth oxide, ZrSi0₄, HfSi0₄, Ti0₂, Ta₂C"5, B₂0₃, 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 Si0₂, A1₂0₃, Zr0₂, Hf0₂, or a rare earth oxide; and at least one of ZrSi0₄, HfSi0₄, Ti0₂, Ta₂0₅, B₂0₃, or an alkali earth metal oxide.

13. The article of claim 12, wherein the bond layer consists essentially of Si; an alkali metal oxide; at least one of Si0₂, A1₂0₃, Zr0₂, Hf0₂, or a rare earth oxide; and at least one of ZrSi0₄, HfSi0₄, Ti0₂, Ta₂0₅, B₂0₃, or an alkali earth metal oxide.

14. The article of claim 13, 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 Si0₂, A1₂0₃, Zr0₂, Hf0₂, or a rare earth oxide; and up to about 20 wt. % of the at least one of ZrSi0₄, HfSi0₄, Ti0₂, Ta₂0₅, B₂0₃, or an alkali earth metal oxide, with a total of 100 wt. %.

15. The article of any of claims 8 to 14, wherein the bond layer has a thickness of less than about 50 μιη.

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 B₂0₃; and

17. The article of claim 16, wherein the bond layer consists essentially of B₂0₃.

18. The article of claim 16, wherein bond layer further comprises at least one of Si, Si0₂, A1₂0₃, Zr0₂, Hf0₂, a rare earth oxide, ZrSi0₄, HfSi0₄, Ti0₂, Ta₂0₅, an alkali metal oxide, or an alkali earth metal oxide.

19. The article of claim 18, wherein the bond layer comprises up to about 20 wt. % B₂0₃ and a balance of the at least one of Si, Si0₂, A1₂0₃, Zr0₂, Hf0₂, a rare earth oxide, ZrSi0₄, HfSi0₄, Ti0₂, Ta₂0₅, 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 Si0₂, A1₂0₃, Zr0₂, Hf0₂, or a rare earth oxide; and at least one of ZrSi0₄, HfSi0₄, Ti0₂, Ta₂Os, 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. % B₂0₃; up to about 50 wt. % Si; up to about 99 wt. % of the at least one of Si0₂, A1₂0₃, Zr0₂, Hf0₂, or a rare earth oxide; and up to about 20 wt. % of the at least one of ZrSi0₄, HfSi0₄, Ti0₂, Ta₂0₅, an alkali metal oxide, or an alkali earth metal oxide, with a total of 100 wt. %.

22. The article of any of claims 16 to 21, wherein the bond layer has a thickness of less than about 50 μιη.

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 Si0₂, Α1₂0₃, Zr0₂, a rare earth oxide, ZrSi0₄, Ti0₂, Ta₂Os, B₂0₃, an alkali metal oxide, or an alkali earth metal oxide.

24. The method of claim 46, 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 Si0₂, A1₂0₃, Zr0₂, a rare earth oxide, ZrSi0₄, Ti0₂, Ta₂0₅, B₂0₃, an alkali metal oxide, or an alkali earth metal oxide.

25. The method of claim 23 or 24, further comprising heat treating the bond layer at between about 1350°C and about 1500°C for up to about 10 hours.

26. The method of claim 25, 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 Si0₂, A1₂0₃, Zr0₂, a rare earth oxide, ZrSi0₄, Ti0₂, Ta₂0₅, B₂0₃, 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°C and about 1500°C for up to about 10 hours to form the bond layer.

27. A method comprising :

forming a bond layer on a substrate comprising a ceramic, a ceramic matrix composite (CMC), or a metal alloy including Si, wherein the bond layer comprises Si; an alkali metal oxide; and at least one of Si0₂, A1₂0₃, Zr0₂, Hf0₂, a rare earth oxide, ZrSi0₄, HfSi0₄, Ti0₂, Ta₂0₅, B₂0₃, or an alkali earth metal oxide.

28. The method of claim 27, wherein forming the bond layer on the substrate comprises forming on the substrate a bond layer consisting essentially of Si; the alkali metal oxide; and the at least one of Si0₂, A1₂0₃, Zr0₂, Hf0₂, a rare earth oxide, ZrSi0₄, HfSi0₄, Ti0₂, Ta₂0₅, B₂0₃, or an alkali earth metal oxide.

29. The method of claim 27 or 28, further comprising heat treating the bond layer at between about 1350°C and about 1500°C for up to about 10 hours.

30. The method of claim 29, 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 Si0₂, A1₂0₃, Zr0₂, Hf0₂, a rare earth oxide, ZrSi0₄, HfSi0₄, Ti0₂, Ta₂0₅,

B₂0₃, 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°C and about 1500°C for up to about

10 hours to form the layer.

31. The method of claim 29, 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 Si0₂, A1₂0₃, Zr0₂, Hf0₂, a rare earth oxide, ZrSi0₄, HfSi0₄, Ti0₂, Ta₂0₅, B₂0₃, 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°C and about 1500°C for up to about 10 hours to form the bond layer.

32. 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 B₂0₃.

33. The method of claim 32, forming the bond layer on the substrate comprises forming on the substrate a bond layer consisting essentially of B₂0₃.

34. The method of claim 32 or 33, further comprising heat treating the bond layer at between about 1350°C and about 1500°C for up to about 10 hours.

35. The method of claim 32 or 34, wherein forming the bond layer on the substrate comprises forming on the substrate a bond layer comprising B₂0₃ and at least one of Si, Si0₂, A1₂0₃, Zr0₂, Hf0₂, a rare earth oxide, ZrSi0₄, HfSi0₄, Ti0₂, Ta₂0₅, an alkali metal oxide, or an alkali earth metal oxide.

36. The method of claim 35, wherein forming on the substrate the bond layer comprising B₂0₃ and the at least one of Si, Si0₂, A1₂0₃, Zr0₂, Hf0₂, a rare earth oxide, ZrSi0₄, HfSi0₄, Ti0₂, Ta₂0₅, an alkali metal oxide, or an alkali earth metal oxide comprises:

forming a first layer comprising B₂0₃ over the substrate,

forming a second layer comprising the at least one of Si, Si0₂, A1₂0₃, Zr0₂,

Hf0₂, a rare earth oxide, ZrSi0₄, HfSi0₄, Ti0₂, Ta₂0₅, an alkali metal oxide, or an alkali earth metal oxide, and

10 hours to form the bond layer.