Binder coating containing metal oxide and oxygen absorber

Abstract

Coated components and methods of forming the same are provided. The coated components include a ceramic matrix composite substrate including silicon carbide and having a surface; a bond coat on the surface of the substrate; and an environmental barrier coating on the bond coat. The bond coat includes a plurality of discrete particles dispersed in a matrix phase including mullite. The plurality of discrete particles includes an oxygen getter and a transition metal oxide.

Description

TECHNICAL FIELD

[0001] The present invention relates generally to bond coats for use with environmental barrier coatings on ceramic components, particularly silicon-based ceramic matrix components, and methods of their formation and use. BACKGROUND

[0002] To improve the efficiency of gas turbine engines, higher operating temperatures for gas turbine engines have been pursued. However, as operating temperatures increase, the high temperature durability of engine components must increase accordingly. Significant advances in high temperature capability have been achieved through the formulation of iron-, nickel-, and cobalt-based high temperature alloys. In addition, for many hot gas path components composed of superalloys, thermal barrier coatings (TBCs) can be used to insulate the components and can maintain an appreciable temperature differential between the load bearing alloy and the coating surface, thereby limiting the thermal exposure of the structural component.

[0003] While superalloys have been found to be widely used for components used throughout the gas turbine engine, particularly for the higher temperature sections, alternative, lighter weight matrix materials such as ceramic matrix composite (CMC) materials, particularly silicon carbide (SiC) fiber reinforced SiC and SiC-Si matrix composites, so-called SiC / SiC composites, have been proposed. CMCs and monolithic ceramic components can be coated with an environmental barrier coating (EBC) to protect them from the harsh environment of a high temperature engine component. The EBC can provide a dense, gas-tight seal against corrosive gases in the high temperature combustion environment.

[0004] Silicon carbide and silicon nitride ceramics undergo oxidation in dry, high temperature environments. This oxidation produces a passivating layer of silicon oxide scale on the surface of the material. In a humid, high temperature, water vapor containing environment, such as a turbine engine, oxidation and recession occurs due to the formation of a passivating layer of silicon oxide scale and subsequent conversion of the silicon oxide to gaseous silicic acid. To prevent recession in a humid, high temperature environment, an environmental barrier coating (EBC) is deposited on the silicon carbide and silicon nitride materials.

[0005] Currently, EBC materials are made from rare earth silicate compounds. These materials seal water vapor, preventing it from reaching the silicon oxide scale on the surface of the silicon carbide or silicon nitride, thereby preventing recession. However, this material does not prevent oxygen permeation, which leads to oxidation of the underlying matrix. Oxidation of the matrix produces a passivating layer of silicon oxide scale, accompanied by the release of carbonaceous oxides or nitrous oxides gases. Carbonaceous oxides (i.e., CO, CO2) or nitrous oxides (i.e., NO, NO2, etc.) gases cannot escape through the dense EBC, thereby forming bubbles, which can cause spallation of the EBC. To date, the use of a silicon bond coat has been the solution to this blistering problem. The silicon bond coat provides a layer that oxidizes (forms a passivating layer of silicon oxide under the EBC) without releasing gaseous byproducts. BRIEF DESCRIPTION OF DRAWINGS

[0006] The complete and enabling disclosure of the present application is set forth in the specification, which includes best modes for carrying out the application, this disclosure being referenced in connection with the accompanying drawings, in which:

[0007] Figure 1 is a cross-sectional schematic view of an exemplary coated component including a bond coat and an EBC thereon;

[0008] Figure 2 is a cross-sectional side view of an exemplary bond coat formed from a substrate having a plurality of discrete particles dispersed therein, including first discrete particles and second discrete particles;

[0009] Figure 3 is a schematic cross-sectional view of an exemplary gas turbine engine in accordance with various embodiments of the present application;

[0010] Figure 4 is a flow diagram of an exemplary method of forming a coated component having a bond coat formed from a substrate having discrete particles dispersed therein;

[0011] Figure 5 shows a cross-sectional view of an exemplary bond coat formed in accordance with embodiments discussed in greater detail below;

[0012] Figure 6 shows a cross-sectional view of an exemplary bond coat formed in accordance with embodiments discussed in greater detail below;

[0013] Figure 7 shows a cross-sectional view of an exemplary bond coat formed in accordance with embodiments discussed in greater detail below;

[0014] Figure 8 shows a cross-sectional view of an exemplary bond coat formed in accordance with embodiments discussed in greater detail below;

[0015] Figure 9 shows a cross-sectional view of a comparative bond coat formed in accordance with embodiments discussed in greater detail below; and

[0016] Figure 10 shows a cross-sectional view of another comparative bond coat formed, discussed in greater detail below.

[0017] Reference numbers repeated in the specification and drawings are intended to refer to the same or like parts or elements throughout the present disclosure.

[0018] DEFINITIONS

[0019] As used herein, the terms "first," "second," and "third" can be used interchangeably to distinguish one component from another and are not intended to signify location or importance of the individual components.

[0020] Chemical elements are discussed in the present disclosure using their common chemical shorthand notation as typically found in the Periodic Table of the Elements. For example, hydrogen is denoted by its common chemical shorthand H; helium is denoted by its common chemical shorthand He; and so forth. As used herein, "RE" means a rare earth element or a mixture of rare earth elements. More specifically, "RE" means a rare earth element of scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), or a mixture thereof.

[0021] As used herein, "alumina" means alumina in the form of AI2O3.

[0022] As used herein, "silica" means silicon oxide in the form of SiO2.

[0023] By contrast, "elemental silicon" means silicon that is present without any alloying materials except incidental impurities. It is sometimes referred to in the art as "silicon metal." Elemental silicon has a melting point of about 1414 °C.

[0024] As used herein, the term "mullite" generally means a mineral that contains alumina and silica. In other words, mullite is a chemical compound of alumina and silica, where the ratio of alumina (AI2O3) and silica (SiO2) is about 3:2 (e.g., the alumina to silica is within 10 mole % of 3:2). However, a ratio of about 2:1 has also been reported as mullite (e.g., the alumina to silica is within 10 mole % of 2:1).

[0025] As used herein, "transition metal" means the metallic elements Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg and the lanthanides (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu).

[0026] As used herein, the term "substantially free of" is understood to mean completely free of, or including trace amounts of, the recited ingredient. "Trace amounts" are quantitative levels of chemical ingredients that are nearly undetectable and provide no benefit to the functional or aesthetic properties of the present compositions. The term "substantially free of" also includes completely free of.

[0027] In the present disclosure, when layers are described as being "on" or "over" another layer or substrate, it is understood that the layers can be in direct contact with each other or have another layer or feature between the layers unless explicitly stated to the contrary. Thus, these terms simply describe the relative position of the layers to each other and do not necessarily imply "over" in the sense of up or down relative position depending on the orientation of the device to the viewer. DETAILED DESCRIPTION

[0028] Reference will now be made in detail to implementations of the present application, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the present application, not limitation of the present application. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present application without departing from the scope of the present application. For instance, features illustrated or described as part of one implementation can be used with another implementation to yield still a further implementation. Thus, it is intended that the present application covers such modifications and variations as come within the scope of the appended claims and their equivalents.

[0029] The presence of the silicon bond coat layer limits the upper working temperature limit of the EBC, as the melting point of silicon metal is relatively low, at about 1414°C. At temperatures above these melting temperatures, the silicon bond coat layer can delaminate from the underlying substrate, effectively removing the bond coat layer and the EBC thereon. Recently, high temperature EBCs have been considered that utilize a bond coat layer containing silicon particles as an oxygen getter.

[0030] However, these high temperature EBCs show weaknesses in the intermediate temperature range. In particular, it is desirable for the bond coat layer to prevent both water and oxygen from permeating to the underlying substrate at temperatures from 650°C to 1500°C. To prevent water permeation, it is desirable to minimize or remove any open porosity in the bond coat layer. Thus, it is desirable to have an improved bond coat layer in the EBC to achieve a higher working temperature limit of the EBC while maintaining effectiveness at lower and intermediate temperatures.

[0031] In principle, liquid phase sintering of the mullite layer can result in densification of the mullite layer. However, residual liquid phase in the layer can result in high oxidant permeability pathways in the mullite, which essentially negates the benefit of the higher density. The methods and coatings described herein address proper composition selection that can densify the mullite through liquid phase sintering, but does not incur significant loss in high and low temperature oxidation life. Thus, the methods and coatings described herein can prevent water permeation by removing open porosity in the EBC through the formation of a densified mullite layer, without incurring significant loss in high and low temperature oxidation life.

[0032] An overall coating component and methods of forming and using the same are provided, the coating component including a bond coat including a matrix phase having a plurality of discrete particles dispersed therein. Generally, the plurality of discrete particles includes an oxygen absorber and a transition metal oxide. Without wishing to be bound by any particular theory, the presence of the transition metal oxide facilitates densification of mullite through liquid phase sintering without causing a significant loss in high and low temperature oxidation life. For example, the methods disclosed herein can remove open porosity in the bond coat by forming a dense mullite layer. In one embodiment, the transition metal oxide adds a specific dopant chemistry to the bond coat that induces liquid phase sintering at sintering temperatures (e.g., 1475 °C to 1565 °C) without causing a significant decrease in oxidation life.

[0033] In one particular embodiment, the bond coat including mullite and the discrete particles is generally located between a substrate surface and an environmental barrier coating (EBC) thereon. Referring to Figure 1 , an exemplary coated component 100 is shown formed from a substrate 102 having a surface 103 with a coating system 106 thereon. Generally, the coating system 106 includes a bond coat 104 on the surface 103 of the substrate and an EBC 108 on the bond coat 104. In the illustrated embodiment, the bond coat 104 is directly on the surface 103 with no intervening layers.

[0034] In Figure 2 the exemplary embodiment, the bond coat 104 is shown having a matrix phase 112 with a plurality of discrete particles 110 dispersed therein. Generally, the plurality of discrete particles 110 includes an oxygen absorber and a transition metal oxide, corresponding to first and second discrete particles 111a and 111b, respectively. Although shown as separate discrete particles 111a and 111b, in certain embodiments, the oxygen absorber and the transition metal oxide can form a mixed particle. In the illustrated embodiment, the matrix phase 112 forms a continuous phase of the bond coat 104. Additionally, in the illustrated embodiment, the matrix phase 112 spans the thickness of the bond coat 104 and is directly bonded to the surface 103 of the substrate 102 and the inner surface 107 of the EBC 108. Figure 1

[0035] ​Generally, a first discrete particle 111a of the plurality of discrete particles 110 includes an oxygen getter configured to react with oxygen during use of the component and to densify the coating during processing so as to inhibit oxygen from reaching the lower surface 103 of the substrate 102. A second discrete particle 111b of the discrete particles 110 of the bond coat includes a transition metal oxide. In most embodiments, the oxygen getter and the transition metal oxide form distinct particles (i.e., the first discrete particle 111a and the second discrete particle 111b). However, in other embodiments, the oxygen getter and the transition metal oxide form a composite particle within the matrix phase 112.

[0036] The transition metal oxide is generally a transition metal oxide (TM x O y where TM is a transition metal, x, y are integers balancing the oxide valence). In one particular embodiment, the transition metal oxide is resistant to chemical reduction to its metallic form (e.g., elemental transition metal), particularly when in the Al2O3-SiO2-TM x O y phase diagram. Generally, any lanthanide oxide has the potential to act as a liquid phase sintering aid, but it is believed that Al2O3-SiO2-TM x O y eutectic compositions at the highest temperatures in the phase diagram are particularly suitable. For example, particularly suitable transition metal oxides can include, but are not limited to, Y2O3, Lu2O3, Sc2O3, TiO2, Ta2O5, La2O3, CeO2, or mixtures thereof.

[0037] The transition metal oxide can be in the form of an elemental oxide, or can be in the form of an aluminate-transition metal oxide complex or a silicate-transition metal oxide complex. In one particular embodiment, for example, the transition metal oxide can be included in an aluminate formed from aluminum oxide and a transition metal oxide (e.g., Al2O3-TM x O y ) to form an aluminate-transition metal oxide complex. In such embodiments, the additional aluminum oxide can sinter with mullite to form an alumina-rich mullite composition. For example, the excess Al2O3 can also form an aluminum oxide (e.g., Al2O3) phase within the mullite. Without wishing to be bound by any particular theory, it is believed that having excess aluminum oxide can help to slow the initial oxidation of the oxygen getter, particularly the processing of the bond coat and the EBC layer overlaid thereon. Additionally, it is believed that complexing the silicon oxide and the transition metal oxide together can result in improved reaction kinetics.

[0038] The oxygen getter and the transition metal oxide can be included in the bond coat in relative amounts sufficient to inhibit oxygen from reaching the underlying surface, to maintain the bond coat with relatively low porosity, and / or to maintain the structural integrity of the bond coat, even at relatively high temperatures. In certain embodiments, the oxygen getter can be included in the bond coat in an amount of 1 wt% to 30 wt%, such as 1 wt% to 10 wt%. In certain embodiments, the transition metal oxide can be included in the bond coat in an amount of 0.1 wt% to 10 wt%, such as 1 wt% to 5 wt%. For example, the transition metal oxide can be included in the bond coat in an amount of 0.1 mol% to 10 mol% of the base material, such as 0.5 mol% to 5 mol%.

[0039] In one embodiment, the oxygen getter includes silicon, such as elemental silicon. For example, the oxygen getter can consist essentially of silicon (at the time the bond coat is formed), such that at least 95 wt% of the oxygen getter is silicon (prior to exposure to any oxygen), such as at least 99 wt% of the oxygen getter.

[0040] In one particular embodiment, the bond coat 104 can be formed from a mixture of a transition metal oxide and elemental silicon (together as discrete particles 110) included within the base phase 112. As explained in more detail below, the elemental silicon within the mullite can melt during operation of the coated component, while remaining included within the base phase and maintaining the functionality of the bond coat 104. Such functionality of the bond coat 104 can include, but is not limited to, bonding the EBC onto a substrate it is bonded to, and absorbing oxygen without releasing a gas to prevent oxidation of the underlying substrate that would otherwise result in a gaseous byproduct. Thus, during operation of the coated component (e.g., in a gas turbine engine), liquid discrete particles can be used within the bond coat 104. Because the bond coat 104 continues to function above the melting point of the discrete particles, the coated component can operate at temperatures above the melting point of the discrete particles.

[0041] While silicon does not oxidize from SiC to a gas such as CO, it does form silicic hydrate gaseous species when in contact with water vapor. However, the partial pressures of the silicic hydrate gaseous species are low enough that they do not significantly form blisters. Furthermore, these partial pressures inhibit blistering unless there are interconnected pores to the external gas surface. The density of the mullite matrix and the gas tightness of the upper layer of the EBC can be controlled to minimize the formation of silicic hydrates.

[0042] In one embodiment, the discrete particles are generally coarse so as to have a size large enough such that the oxidation reaction occurs relatively slowly throughout the thickness of the bond coat. Without wishing to be bound by any particular theory, it is believed that oxidation occurs only on a thin surface layer of the coarser particles, effectively slowing the oxidation of the discrete particles as compared to finer particles. Thus, the presence of relatively coarse particles can result in a more controllable stress state as compared to finer particles, resulting in less propensity for cracking. Additionally, the oxidation of the coarser particles can result in a diffusion reaction zone within the thickness of the bond coat, rather than a sharp reaction front that can be seen in the case of smaller particles. Furthermore, the discrete particles undergo oxidation or evaporation during the manufacturing process of the coating. Coarser particles provide the advantage of slowing this degradation, thus can help maintain the desired proportion of particles in the bond coat.

[0043] As noted above, the plurality of discrete particles have a relatively large size (i.e., coarse particles) such that the oxidation reaction of the oxygen getter occurs relatively slowly throughout the thickness of the bond coat. However, if the size of the discrete particles 110 is too large and / or the content is too high, the discrete particles can form a continuous phase when used at the temperature at which the oxygen getter liquefies (e.g., above 1414 °C when silicon is included). Too much of a continuous phase (formed by liquefied discrete particles that are too large) can result in spalling of the coating.

[0044] For example, greater than 50% by volume (e.g., greater than 75% by volume) of the plurality of discrete particles are formed of particles having an average size of 10 pm to 100 pm. In one embodiment, greater than 50% by volume (e.g., greater than 75% by volume) of the plurality of discrete particles are formed of particles having an average size of 20 pm to 75 pm. In a particular embodiment, greater than 50% by volume (e.g., greater than 75% by volume) of the plurality of discrete particles are formed of particles having an average size of 30 pm to 50 pm. Thus, without wishing to be bound by any particular theory, it is believed that the presence of these relatively large particles slows the oxidation reaction to result in a diffusion reaction zone, resulting in reduced stress and inhibition of cracking due to expansion.

[0045] Regardless of the configuration of the bond coat 104, upon melting of the oxygen getter, the discrete particles 110 are contained within the bulk phase 112 between the surface 103 of the substrate 102 and the inner surface 107 of the environmental barrier coating 108. In other words, the bulk phase 112 can form a three-dimensional network spanning the thickness of the bond coat 104 and is bonded to the surface 103 of the substrate 102 and the inner surface 107 of the environmental barrier coating 108. In this way, the bulk phase 112 works with the surface 103 of the substrate 102 and the environmental barrier coating 108 to contain the melted oxygen getter therein while maintaining the integrity of the bond coat 104 without delaminating from the surface 103 of the substrate 102.

[0046] Accordingly, the matrix phase 112 is included in the bond coat 104 in an amount to provide structural integrity to the bond coat 104 while the oxygen getter of the discrete particles 110 melts at the operating temperature, such as when the oxygen getter is silicon, at temperatures above the melting point of elemental silicon (i.e., about 1414 °C), while introducing a sufficient amount of the oxygen getter therein. The matrix phase 112 also serves to limit the diffusion of oxidizing agents (i.e., oxygen or water vapor) to the discrete particles 110. In one embodiment, the matrix phase can comprise at least 60 vol% of the bond coat 104 (e.g., at least 60 vol% of the bond coat 104 can comprise mullite). In particular embodiments, the bond coat 104 can comprise from 60 vol% to 98 vol% of the matrix phase (e.g., mullite), such as from 65 vol% to 96 vol% of the matrix phase (e.g., mullite), such as from 75 vol% to 95 vol% of the matrix phase (e.g., mullite).

[0047] In contrast, the oxygen getter of the discrete particles 110 is included in the bond coat 104 in an amount sufficient to act as an oxygen getter to inhibit oxygen from reaching the underlying substrate 102. In one particular embodiment, the oxygen getter can be formed from silicon metal (i.e., elemental silicon), a silicon alloy (e.g., a silicon eutectic alloy), a suicide, or a mixture thereof. Accordingly, when the bond coat 104 reaches a temperature of about 1400 °C to about 2550 °C, depending on the composition of the oxygen getter, the oxygen getter can melt. In some embodiments, the matrix phase 112 comprises mullite and has a melting point of about 1825 °C to 1890 °C. In some cases, the temperature of the bond coat 104 can be above the melting point of the oxygen getter, but below the melting point of the matrix phase 112, such that the oxygen getter becomes molten. For example, the oxygen getter can have a melting temperature of about 1414 °C (i.e., the melting point of elemental silicon) to about 1485 °C. In particular embodiments, the oxygen getter can be formed from a silicon material that melts at a bond coat temperature of 1415 °C, 1450 °C, 1550 °C, and / or 1600 °C.

[0048] For example, in certain embodiments, the bond coat 104 can comprise from 2 vol% to 40 vol% of the discrete particles 110 (i.e., the total volume of the mixture of the oxygen getter and the transition metal oxide), such as from 4 vol% to 35 vol% of the discrete particles 110 (e.g., from 5 vol% to 25 vol% of the discrete particles 110).

[0049] In certain embodiments, suicides having a melting point of about 1900 °C or less (e.g., from about 1400 °C to about 1900 °C) can also be present in the discrete particles 110 as the oxygen getter. The melting point of a particular suicide can be readily determined using the Si phase diagram.

[0050] In particular embodiments, the oxygen getter within the discrete particles can have minimal thermal expansion coefficient mismatch (e.g., no more than about 2-3 ppm per °C) with the matrix and mullite to avoid matrix cracking. However, one skilled in the art will recognize that greater expansion coefficient mismatch can be accommodated by reducing the volume fraction of the getter phase. In another particular embodiment, the oxygen getter should have minimal volume increase upon oxidation (e.g., no more than 150%, preferably no more than 100%, more preferably a volume decrease rather than a volume expansion upon oxidation) to reduce stresses and cracking in the mullite layer. Numerous embodiments of the discrete particles are possible that satisfy the requirements for expansion coefficient mismatch and volume change upon oxidation. In one embodiment, the oxygen getter comprises elemental silicon, and can be pure elemental silicon. In another embodiment, the oxygen getter comprises a silicon alloy and / or a silicide. In embodiments where the oxygen getter comprises elemental silicon, the bond coat can be referred to as a "mullite / Si bond coat." When silicon is oxidized to form amorphous silica, it expands in volume by about 115% to about 130%, and when silicon is oxidized to form crystalline silica, it expands in volume by about 85%. However, the oxidation product is first constant amorphous, which can then change to crystalline over time.

[0051] Other embodiments of the oxygen getter can include, but are not limited to, nickel, cobalt, chromium, or mixtures thereof. These oxygen getters can also be used in particular embodiments with silicon, silicon alloys, and / or silicides. For example, nickel has a much higher expansion mismatch with the matrix and mullite (almost 8 ppm / °C). Thus, the maximum volume fraction of nickel that can be tolerated will be lower than the maximum volume fraction of silicon, which has a mismatch of less than 1 ppm / °C. However, nickel expands in volume upon oxidation by about 65%, in contrast to silicon, which expands in volume by about 115% to about 130% when converted to amorphous silica. On the other hand, chromium has a lower expansion mismatch with the matrix and mullite than nickel. Chromium also has a higher melting temperature (1907 °C) than silicon (1410 °C) and nickel (1455 °C).

[0052] The matrix phase 112 can include an oxide material, particularly an oxide material having a melting temperature higher than the melting temperature of the oxygen getter. Additionally, the matrix phase 112 can include an oxide material that is generally non-reactive with the oxygen getter of the discrete particles 110, even at elevated operating temperatures. In one particular embodiment, the matrix phase 112 is formed of crystalline mullite having a melting temperature higher than the melting temperature of the oxygen getter. In particular embodiments, the mullite has a melting temperature of about 1825 °C to 1890 °C and is generally non-reactive with the oxygen getter and / or transition metal oxide of the discrete particles 110.

[0053] In one embodiment, the matrix phase 112 can include mullite with an excess of alumina (up to about 10 mole percent excess alumina). For example, the matrix phase 112 can include mullite formed from alumina and silica in a stoichiometric ratio of about 3:2 to about 3.5:2, or in a stoichiometric ratio of about 2: 1 to about 2.25: 1. In another embodiment, the matrix phase 112 can include mullite with an excess of silica.

[0054] Mullite generally has a relatively slow diffusion rate for oxygen at all temperatures of interest (even up to 1650°C, e.g., 1200°C to 1650°C). At temperatures above 1200°C, the only other crystalline oxide believed to have a lower oxygen diffusion rate than mullite is alumina, which has a very high coefficient of thermal expansion compared to the matrix and cannot be deposited as a dense coating without spalling. Although the coefficient of thermal expansion ("CTE") of mullite is similar to the CTE of the SiC CMC matrix 102, the CTE of mullite is not an exact match to SiC. If the bond coat 104 is too thick, the slight mismatch in CTE of mullite and SiC can cause problems related to thermal expansion, such as cracking and / or delamination. For example, a bond coat 104 having a thickness of 20 mils (i.e., 508 μm) is believed to cause problems related to the CTE mismatch after repeated exposure to service temperatures. On the other hand, a bond coat 104 having a maximum thickness of 15 mils or less, e.g., 1 mil to 15 mils (i.e., 381 μm or less, e.g., 25.4 μm to 381 μm), is believed to survive such service temperatures without significant problems from the CTE mismatch. In one particular embodiment, the bond coat 104 has a maximum thickness of 10 mils, e.g., 3 mils to 10 mils (i.e., 127 μm, e.g., 76.2 μm to 254 μm).

[0055] As noted above, the combination of oxygen getters and transition metal oxides in the mullite-based matrix phase results in a bond coat having a relatively low porosity. In one embodiment, the bond coat has a porosity of less than 15%, as measured according to ASTM E2109-01.

[0056] In one particular embodiment, the substrate 102 is formed from a ceramic matrix composite material ("CMC"). As used herein, a ceramic matrix composite or "CMC" refers to a class of materials that include a reinforcing material (e.g., reinforcing fibers) surrounded by a ceramic matrix phase. Typically, the reinforcing fibers provide structural integrity to the ceramic matrix. Some examples of matrix materials for CMCs can include, but are not limited to, non-oxide silicon matrix materials (e.g., silicon carbide, silicon nitride, or mixtures thereof), oxide ceramics (e.g., silicon oxycarbide, silicon oxynitride, alumina (AI2O3), silica (SiO2), siluminas, or mixtures thereof), or mixtures thereof. Optionally, ceramic particles (e.g., oxides of Si, Al, Zr, Y, and combinations thereof) and inorganic fillers (e.g., pyrophyllite, wollastonite, mica, talc, kyanite, and montmorillonite) can also be included within the CMC matrix.

[0057] Some examples of reinforcing fibers for CMCs can include, but are not limited to, non-oxide silicon matrix materials (e.g., silicon carbide, silicon nitride, or mixtures thereof), non-oxide carbon matrix materials (e.g., carbon), oxide ceramics (e.g., silicon oxycarbide, silicon oxynitride, alumina (AI2O3), silica (SiO2), siluminas such as mullite, or mixtures thereof), or mixtures thereof.

[0058] Typically, particular CMCs can be referred to by their combination of fiber type / matrix type. For example, carbon fiber reinforced silicon carbide is referred to as C / SiC; silicon carbide fiber reinforced silicon carbide is referred to as SiC / SiC; silicon carbide fiber reinforced silicon nitride is referred to as SiC / SiN; silicon carbide fiber reinforced silicon carbide / silicon nitride matrix mixtures are referred to as SiC / SiC-SiN, etc. In other examples, CMCs can be composed of a matrix and reinforcing fibers that include oxide-based materials, such as alumina (AI2O3), silica (SiO2), siluminas, and mixtures thereof. Siluminas can include crystalline materials, such as mullite (3AI2O3 2SiO2), as well as glassy siluminas.

[0059] In certain embodiments, the reinforcing fibers can be bundled and / or coated prior to inclusion within the matrix. For example, fiber tows can be formed into reinforcing tapes, such as unidirectional reinforcing tapes. Multiple tapes can be layered together to form a preform. The fiber tows can be impregnated with a slurry composition prior to forming the preform or after forming the preform. The preform can then be heat treated, such as cured or burned out, to produce a high carbon residue in the preform, and subsequently chemically treated, such as with silicon melt infiltration, to obtain a part formed from a CMC material having a desired chemical composition.

[0060] Such materials are particularly suitable for higher temperature applications with certain monolithic ceramics (i.e., ceramic materials without a reinforcing material). Additionally, these ceramic materials are lighter in weight compared to superalloys, yet still provide strength and durability to components made therefrom. As such, such materials are currently being considered for use in many gas turbine engine components used in the higher temperature portions of gas turbine engines, such as vanes (e.g., turbine vanes and blades), combustors, shrouds, and other similar components, which would benefit from the lighter weight and higher temperature capability that these materials can provide.

[0061] As used herein, an environmental barrier coating or "EBC" refers to a coating system comprising one or more layers of ceramic material, each layer of ceramic material providing specific or multifunctional protection to the underlying CMC. An EBC typically includes multiple layers, such as a rare earth silicate coating (e.g., a rare earth disilicate, such as a slurry or APS-deposited yttrium- ytterbium disilicate (YbYDS)), an alkaline earth aluminosilicate (e.g., comprising barium-strontium-aluminum silicate (BSAS), such as having a range of BaO, SrO, AI2O3, and / or SiO2compositions), an air-tight layer (e.g., a rare earth disilicate), and / or an outer coating (e.g., comprising a rare earth monosilicate, such as a slurry or APS-deposited yttrium monosilicate (YMS)). One or more of the layers can be doped as desired, and the EBC can also be coated with a wear-resistant coating.

[0062] As noted above, the bond coat 104 can be used in conjunction with an EBC 108 to form a coated component 100 having an increased operating temperature compared to using a silicon bond coat alone (without a matrix phase). The EBC 108 can include one or more layers in any combination formed from materials selected from typical EBC or thermal barrier coating ("TBC") layer chemistries, including but not limited to rare earth silicates (e.g., monosilicates and disilicates), aluminosilicates (e.g., mullite, barium strontium silicate aluminate (BSAS), rare earth aluminosilicates, etc.), hafnia, zirconia, stabilized hafnia, stabilized zirconia, rare earth hafnates, rare earth zirconates, rare earth gallium oxides, etc. The EBC can include a hafnia layer, an alumina layer, or both. Alternatively or additionally, the EBC can include a rare earth disilicate layer, a rare earth monosilicate layer, or both.

[0063] The EBC 108 can be formed from a plurality of individual layers 114. In the illustrated embodiment, the EBC 108 includes a hermetic layer 116 disposed directly on the bond coat 104 so as to encapsulate the oxygen absorber of the discrete particles 110 within the bond coat 104 upon melting. In one embodiment, the hermetic layer is made of mullite up to 2 mils thick, such as preferably about 0.1 mil to about 1 mil thick (e.g., about 0.1 mil to about 0.5 mil thick). As the oxygen absorber of the discrete particles 110 reacts with oxygen (e.g., forming silicon oxide), there is minimal gaseous oxide (e.g., carbon oxide) produced upon exposure of the component 100 to oxygen at operating temperatures. Thus, a gas escape layer through the bond coat 104 is not required, and the hermetic layer can be included within the EBC 108. It is even desirable to have a hermetic layer to prevent water vapor from entering the bond coat 104. In one embodiment, the hermetic layer 116 can be located directly on the bond coat 104, but can also be located elsewhere within the EBC 108.

[0064] The coated component 100 is particularly suitable for use as a component in a high temperature environment, such as those components present in a gas turbine engine, such as combustor components, turbine blades, shrouds, nozzles, heat shields, and vanes. In particular, the coated component 100 can be a CMC component located within a hot gas path of a gas turbine engine, such that the coating system 106 forms an environmental barrier for the underlying substrate 102 to protect the component 100 within the gas turbine engine upon exposure to the hot gas path. In certain embodiments, the bond coat 104 is configured such that the coated component 100 is exposed to operating temperatures of about 1475 °C to about 1650 °C, while the bond coat 104 remains substantially unaffected by such operating temperatures. Thus, the bond coat 104 can withstand exposure to operating temperatures of about 1475 °C to about 1650 °C.

[0065] Figure 3 is a schematic cross-sectional view of a gas turbine engine according to an example embodiment of the present disclosure. More specifically, for embodiments of Figure 3 The gas turbine engine is a high-bypass turbofan engine 10, hereinafter referred to simply as "turbine engine 10." As shown in Figure 3As shown, the turbofan engine 10 defines an axial direction A (extending parallel to the longitudinal axis 12 for reference) and a radial direction R. Generally, the turbofan engine 10 includes a fan section 14 and a core turbine engine 16 disposed downstream from the fan section 14. Although described below with reference to a turbofan engine 10, the present disclosure can apply to turbomachinery in general, including turbojet, turboprop, and turboshaft engines, including industrial and marine gas turbine engines, as well as auxiliary power units. It can also apply to other high temperature applications containing water vapor in the gas phase, such as those resulting from the combustion of hydrocarbon fuels.

[0066] The exemplary core turbine engine 16 as shown generally includes a substantially tubular outer casing 18 defining an annular inlet 20. The casing 18 encloses, in serial flow relationship, a compressor section including a booster or low pressure (LP) compressor 22 and a high pressure (HP) compressor 24; a combustion section 26; a turbine section including a high pressure (HP) turbine 28 and a low pressure (LP) turbine 30; and a jet exhaust nozzle section 32. A high pressure (HP) spool or shaft 34 drivingly connects the HP turbine 28 to the HP compressor 24. A low pressure (LP) spool or shaft 36 drivingly connects the LP turbine 30 to the LP compressor 22.

[0067] For the embodiment shown, the fan section 14 includes a variable pitch fan 38 having a plurality of blades 40 connected to a disk 42 in a spaced apart manner. As shown, the blades 40 generally extend outwardly from the disk 42 along the radial direction R. Since the blades 40 are operably connected to appropriate actuating members 44 configured to collectively and uniformly change the pitch of the blades 40, each blade 40 is rotatable about a pitch axis P relative to the disk 42. The blades 40, disk 42, and actuating members 44 are together rotatable about the longitudinal axis 12 across the LP shaft 36 by an optional power gearbox 46. The power gearbox 46 includes a plurality of gears for reducing the rotational speed of the LP shaft 36 to a more efficient rotational fan speed.

[0068] Still referring to the exemplary embodiment of Figure 3 The disk 42 is covered by a rotatable forward nacelle 48 that is aerodynamically shaped to facilitate airflow through the plurality of blades 40. Additionally, the exemplary fan section 14 includes an annular fan case or outer nacelle 50 that circumferentially surrounds at least a portion of the fan 38 and / or the core turbine engine 16. It should be appreciated that the nacelle 50 can be configured to be supported relative to the core turbine engine 16 by a plurality of circumferentially spaced apart outlet guide vanes 52. Moreover, a downstream portion 54 of the nacelle 50 can extend over an exterior of the core turbine engine 16 so as to define a bypass airflow passage 56 therebetween.

[0069] During operation of the turbofan engine 10, a volume of air 58 enters the turbofan engine 10 through an associated inlet 60 of the nacelle 50 and / or fan section 14. As the volume of air 58 passes through the fan blades 40, a first portion of the air, as indicated by arrow 62, is directed or channeled into the bypass airflow passage 56, while a second portion of the air, as indicated by arrow 64, is directed or channeled into the LP compressor 22. The ratio between the first portion of air 62 and the second portion of air 64 is commonly referred to as the bypass ratio. The pressure of the second portion of air 64 is then increased as it passes through the high pressure (HP) compressor 24 and into the combustion section 26, where it is mixed with fuel and burned to provide combustion gases 66.

[0070] The combustion gases 66 are directed through the HP turbine 28, where a portion of the thermal and / or kinetic energy from the combustion gases 66 is extracted via successive stages of HP turbine stator vanes 68, which are connected to the outer casing 18, and HP turbine rotor vanes 70, which are connected to the HP spool or shaft 34, thus rotating the HP spool or shaft 34 to support operation of the HP compressor 24. The combustion gases 66 are then directed through the LP turbine 30, where a second portion of the thermal and kinetic energy is extracted from the combustion gases 66 via successive stages of LP turbine stator vanes 72, which are connected to the outer casing 18, and LP turbine rotor vanes 74, which are connected to the LP spool or shaft 36, thus rotating the LP spool or shaft 36 to support operation of the LP compressor 22 and / or rotation of the fan 38.

[0071] The combustion gases 66 are subsequently directed through the jet exhaust nozzle section 32 of the core turbine engine 16 to provide propulsive thrust. At the same time, the pressure of the first portion of air 62 is significantly increased as the first portion of air 62 passes through the bypass airflow passage 56 before being exhausted from a fan nozzle exhaust section 76 of the turbofan engine 10, also providing propulsive thrust. The HP turbine 28, the LP turbine 30, and the jet exhaust nozzle section 32 at least partially define a hot gas path 78 for directing the combustion gases 66 through the core turbine engine 16.

[0072] Methods for coating ceramic components are also generally provided. For example, Figure 4An example method 400 of forming a coating system on a surface of a substrate is shown. At 402, a bond coat is formed on a surface of a substrate to include discrete particles contained in a matrix phase, as described above with respect to bond coat 104. In one embodiment, the bond coat is formed by air plasma spraying. In another embodiment, it is formed by suspension plasma spraying, in which a liquid suspension of the desired chemical formulation is used for the air plasma spray. In another embodiment, the coating is formed by low pressure plasma spraying. In another embodiment, one or more coated layers can be formed by slurry coating methods followed by sintering the layer. Different coatings can be formed by one or more of these methods.

[0073] At 404, an environmental barrier coating (EBC) is formed on the bond coat. As described above, the discrete particles, when melted, are contained in a matrix phase between the surface of the substrate and the inner surface of the environmental barrier coating.

[0074] Examples

[0075] An example bond coat material was prepared using a mixture of an oxygen getter and a transition metal oxide dispersed in a continuous mullite phase, and a comparative bond coat material was prepared without the transition metal oxide.

[0076] Figure 5 A picture of a pellet containing the example bond coat material is shown after a thermal test. The pellet containing the example bond coat material was formed from 75.5 wt% mullite as the matrix material, 12.7 wt% AI2O3 to alumina-rich the mullite, 9.6 wt% elemental silicon as the oxygen getter, and 2.1 wt% Lu2O3 as the transition metal oxide. The example bond coat material was formed by cold pressing a powder mixture of the mullite, AI2O3, silicon, and Lu2O3 into a pellet, followed by pressureless sintering. The bond coat material was used as the example bond coat material, even though it was not a coating. The pellet was then subjected to a thermal test in air at a temperature of 1480°C to 1540°C for 10 hours to determine whether porosity would develop within the layer. As shown, the porosity within the pellet was substantially eliminated, even after the thermal test.

[0077] Figure 6A picture of a pellet containing an exemplary bond coat material after thermal testing is shown. The pellet containing the exemplary bond coat material was formed from 76.6 wt% mullite as the matrix material, 12.9 wt% AI2O3 to alumina-rich the mullite, 9.8 wt% elemental silicon as the oxygen getter, and 0.7 wt% Sc2O3 as the transition metal oxide. The exemplary bond coat material was formed by cold pressing a powder mixture of mullite, AI2O3, silicon, and Sc2O3 into a pellet, followed by pressureless sintering. The bond coat material was used as the exemplary bond coat material even though it was not a coating. The pellet was then subjected to thermal testing in air at a temperature of 1480°C to 1540°C for 10 hours to determine whether porosity would develop within the layer. As shown, the porosity within the pellet was very small even after thermal testing.

[0078] Figure 7 A picture of a pellet containing an exemplary bond coat material after thermal testing is shown. The pellet containing the exemplary bond coat material was formed from 76.5 wt% mullite as the matrix material, 12.8 wt% AI2O3 to alumina-rich the mullite, 9.8 wt% elemental silicon as the oxygen getter, and 0.9 wt% TiO2 as the transition metal oxide. The exemplary bond coat material was formed by cold pressing a powder mixture of mullite, AI2O3, silicon, and TiO2 into a pellet, followed by pressureless sintering. The bond coat material was used as the exemplary bond coat material even though it was not a coating. The pellet was then subjected to thermal testing in air at a temperature of 1480°C to 1540°C for 10 hours to determine whether porosity would develop within the layer. As shown, the porosity within the pellet was very small even after thermal testing.

[0079] Figure 8 A cross-sectional picture of an exemplary bond coat material after thermal testing is shown. The exemplary bond coat material was formed by solution plasma spraying 85 vol% mullite as the matrix material, 10 wt% AI2O3 (compared to the total weight of mullite and silicon) to alumina-rich the mullite, 15 vol% elemental silicon as the oxygen getter, and 3.2 wt% Lu2Si2O7 (compared to the total weight of mullite and silicon) as the transition metal oxide. The solid portion used for solution plasma spraying was: 77 wt% mullite, 11 wt% Si, 9 wt% AI2O3, and 3 wt% Lu2Si2O7. The coating was then subjected to thermal testing in air at a temperature of 1540°C for 10 hours to determine whether porosity would develop within the layer. As shown, the porosity within the bond coat was almost eliminated even after thermal testing.

[0080] Figure 9A photograph of a pellet comprising a comparative bond coat material but in the absence of any transition metal oxide after a thermal test is shown. The pellet comprising the comparative bond coat material was formed from 77.1 wt% mullite as the matrix material, 13 wt% AI2O3 to aluminate the mullite, and 9.9 wt% elemental silicon as the oxygen getter. The comparative bond coat material was formed by cold pressing a powder mixture of mullite, AI2O3, and silicon into a pellet, followed by pressureless sintering. The comparative bond coat material was formed in the same manner as the pellets described above for Examples 1-7, but in the absence of any transition metal oxide. The pellet was then subjected to a thermal test in air at a temperature of 1480°C to 1540°C for 10 hours to determine whether porosity would develop within the layer. As shown in the photograph, Figure 5 , 6 and 7, but in the absence of any transition metal oxide. The pellet was then subjected to a thermal test in air at a temperature of 1480°C to 1540°C for 10 hours to determine whether porosity would develop within the layer. As shown in the photograph, Figure 9 , there was significant open porosity present in the comparative pellet after the thermal test.

[0081] Figure 10 A cross-sectional view of the comparative bond coat material after the thermal test is shown. The comparative bond coat material was formed by solution plasma spraying 85 vol% mullite as the matrix material, 10 wt% AI2O3 (compared to the total weight of mullite and silicon) to aluminate the mullite, and 15 vol% elemental silicon as the oxygen getter. The solid portion used for the solution plasma spraying was: 79 wt% mullite, 12 wt% Si, and 9 wt% AI2O3. The comparative bond coat was formed in the same manner as the coating described above for Example 8, Figure 8 , but in the absence of any transition metal oxide. The coating was then subjected to a thermal test in air at a temperature of 1540°C for 10 hours to determine whether porosity would develop within the layer. As shown in the photograph, the porosity within the bond coat after the thermal test was much greater than the porosity shown in the exemplary bond coat of Figure 8 .

[0082] Aspects of the present disclosure prevent water permeation by removing the open pores in the EBC by forming a dense mullite layer, without causing a significant loss in high and low temperature oxidation life.

[0083] Other aspects of the present invention are provided by the subject matter of the following clauses:

[0084] A coated component comprising: a ceramic matrix composite substrate comprising silicon carbide and having a surface; a bond coat on the surface of the substrate, the bond coat comprising a plurality of discrete particles dispersed in a matrix phase, the plurality of discrete particles comprising an oxygen-getter and a transition metal oxide, the matrix phase comprising mullite; and, an environmental barrier coating on the bond coat.

[0085] The coated component of any of the preceding clauses, wherein the transition metal oxide comprises Y2O3, Lu2O3, Sc2O3, TiO2, Ta2O5, La2O3, CeO2, or mixtures thereof.

[0086] The coated component of any of the preceding clauses, wherein the bond coat comprises 0.1 wt% to 10 wt% of the transition metal oxide.

[0087] The coated component of any of the preceding clauses, wherein the bond coat has a porosity of less than 15%.

[0088] The coated component of any of the preceding clauses, wherein the oxygen getter forms a first discrete particle of the plurality of discrete particles and the transition metal oxide forms a second discrete particle of the plurality of discrete particles.

[0089] The coated component of any of the preceding clauses, wherein the oxygen getter comprises elemental silicon, a silicon alloy, a silicide, or mixtures thereof.

[0090] The coated component of any of the preceding clauses, wherein the oxygen getter comprises elemental silicon.

[0091] The coated component of any of the preceding clauses, wherein the bond coat comprises 1 wt% to 30 wt% of the oxygen getter.

[0092] The coated component of any of the preceding clauses, wherein the matrix phase is a continuous phase that spans the bond coat and is directly bonded to the surface of the substrate and the inner surface of the environmental barrier coating.

[0093] The coated component of any of the preceding clauses, wherein the matrix phase comprises 60 vol% to 98 vol% of the bond coat.

[0094] The coated component of any of the preceding clauses, wherein the matrix phase comprises 65 vol% to 96 vol% of the bond coat.

[0095] The coated component of any of the preceding clauses, wherein the matrix phase comprises 75 vol% to 95 vol% of the bond coat.

[0096] The coated component of any of the preceding clauses, wherein the matrix phase consists essentially of mullite.

[0097] The coated component of any of the preceding clauses, wherein the environmental barrier coating comprises a plurality of layers, at least one layer of the plurality of layers of the environmental barrier coating comprising an air-tight layer.

[0098] The coated component of any of the preceding clauses, wherein the air-tight layer is adjacent to the bond coat such that the air-tight layer defines the inner surface of the environmental barrier coating.

[0099] The coated component of any of the preceding clauses, wherein the bond coat is configured to withstand exposure to operating temperatures of 1475 °C to 1650 °C.

[0100] The coated component of any of the preceding clauses, wherein the environmental barrier coating comprises a hafnium dioxide layer, an aluminum oxide layer, or both.

[0101] The coated component of any of the preceding clauses, wherein the environmental barrier coating comprises a rare earth disilicate layer, a rare earth monosilicate layer, or both.

[0102] A method of forming a coated component of any of the preceding clauses.

[0103] A method of forming a coated component, the method comprising: forming a bond coat on a surface of a substrate, the bond coat comprising a plurality of discrete particles dispersed in a matrix phase, the plurality of discrete particles comprising an oxygen absorber and a transition metal oxide, the matrix phase comprising mullite; and forming an environmental barrier coating on the bond coat such that the plurality of discrete particles are contained in the matrix phase between the surface of the substrate and an inner surface of the environmental barrier coating upon melting.

[0104] The method of any of the preceding clauses, wherein the transition metal oxide comprises Y2O3, Lu2O3, Sc2O3, TiO2, Ta2O5, La2O3, CeO2, or mixtures thereof.

[0105] This specification discloses the invention by using examples, including the best mode, and also enables those skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patent scope of the invention is defined by the claims, and can include other examples that occur to those skilled in the art. Such other examples are within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

Claims

1. A coated component comprising: a ceramic matrix composite substrate comprising silicon carbide and having a surface; a bond coat on a surface of the ceramic matrix composite substrate, the bond coat comprising a plurality of discrete particles dispersed in a matrix phase, the plurality of discrete particles comprising an oxygen absorber and a transition metal oxide in the form of an aluminate-transition metal oxide complex, the matrix phase comprising mullite, the bond coat having a thickness of 25.4 - 381 micrometers, the bond coat comprising 0.1 wt% to 10 wt% of the transition metal oxide and 1 wt% to 30 wt% of the oxygen absorber; and an environmental barrier coating on the bond coat; the matrix phase is located between the surface of the ceramic matrix composite substrate and an inner surface of the environmental barrier coating.

2. The coated component of claim 1, wherein, the transition metal oxide comprises Y2O3, Lu2O3, Sc2O3, TiO2, Ta2O5, La2O3, CeO2, or mixtures thereof.

3. The coated component of claim 1, wherein, the bond coat has a porosity of less than 15%.

4. The coated component of claim 1, wherein, the oxygen getter forms a first discrete particle of the plurality of discrete particles and the transition metal oxide forms a second discrete particle of the plurality of discrete particles.

5. The coated component of claim 1, wherein, the oxygen getter comprises elemental silicon, a silicon alloy, a silicide, or mixtures thereof.

6. The coated component of claim 1, wherein, the oxygen getter comprises elemental silicon.

7. The coated component of claim 1, wherein, the matrix phase is a continuous phase that spans the bond coat and is directly bonded to the surface of the ceramic matrix composite substrate and the inner surface of the environmental barrier coating.

8. The coated component of claim 1, wherein, the matrix phase comprises 60 to 98 volume percent of the bond coat.

9. The coated component of claim 1, wherein, the matrix phase comprises 65 to 96 volume percent of the bond coat.

10. The coated component of claim 1, wherein, the matrix phase comprises 75 to 95 volume percent of the bond coat.

11. The coated component of claim 1, wherein, the matrix phase consists essentially of mullite.

12. The coated component of claim 1, wherein, the environmental barrier coating comprises a plurality of layers, at least one layer of the plurality of layers of the environmental barrier coating comprises a gas tight layer.

13. The coated component of claim 12, wherein, the gas tight layer is adjacent to the bond coat such that the gas tight layer defines the inner surface of the environmental barrier coating.

14. The coated component of claim 1, wherein, the bond coat is configured to withstand exposure to a service temperature of 1475°C to 1650°C.

15. The coated component of claim 1, wherein, the environmental barrier coating comprises a hafnium dioxide layer, an aluminum oxide layer, or both.

16. The coated component of claim 1, wherein, the environmental barrier coating comprises a rare earth disilicate layer, a rare earth monosilicate layer, or both.

17. A method of forming a coated component, the method comprising: forming a bond coat on a surface of a substrate, the bond coat comprising a plurality of discrete particles dispersed in a matrix phase, the plurality of discrete particles comprising an oxygen getter and a transition metal oxide in the form of an aluminate-transition metal oxide complex, the matrix phase comprising mullite, the bond coat having a thickness of 25.4 - 381 micrometers, the bond coat comprising 0.1 to 10 weight percent of the transition metal oxide and 1 to 30 weight percent of the oxygen getter; and forming an environmental barrier coating on the bond coat such that the plurality of discrete particles are contained in the matrix phase located between the surface of the substrate and an inner surface of the environmental barrier coating upon melting.

18. The method of claim 17, wherein, the transition metal oxide comprises Y2O3, Lu2O3, Sc2O3, TiO2, Ta2O5, La2O3, CeO2, or mixtures thereof.

Images