Bond coat containing metal oxide and oxygen getter

Abstract

To provide coated components (100) and their methods of formation.SOLUTION: A coated component (100) includes: a ceramic matrix composite substrate (102) comprising silicon carbide and having a surface (103); a bond coat (104) on the surface (103) of the substrate (102); and an environmental barrier coating (108) on the bond coat (104). The bond coat (104) includes a plurality of discrete particles (110) dispersed within a matrix phase (112) that includes mullite. The plurality of discrete particles (110) includes an oxygen getter and a transition metal oxide.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] This invention relates generally to bond coats for use with environmental barrier coatings on ceramic components, particularly silicon-based ceramic matrix components, and methods of forming and using same. [Background technology]

[0002]

[0002] Higher operating temperatures are continually sought to improve the efficiency of gas turbine engines. However, as operating temperatures increase, the high temperature durability of the engine's components must correspondingly increase. Significant advances in high temperature performance have been achieved with the formation of superalloys based on iron, nickel, and cobalt. Nevertheless, many hot gas path components constructed from superalloys can utilize thermal barrier coatings (TBCs) to insulate the components and maintain a significant temperature differential between the load-bearing alloy and the coating surface, thus limiting the thermal exposure of the structural components.

[0003]

[0003] Although superalloys are widely used throughout gas turbine engines, especially for components used in the hot sections, alternative lightweight substrate materials have been proposed, such as ceramic matrix composite (CMC) materials, especially silicon carbide fiber reinforced SiC and SiC-Si matrix composites, so-called SiC / SiC composites. CMCs and monolithic ceramic components can be coated with environmental barrier coatings (EBCs) to protect them from the harsh environment of the hot engine parts. EBCs can provide a dense hermetic seal against corrosive gases in the high temperature combustion environment.

[0004]

[0004] Silicon carbide and silicon nitride ceramics undergo oxidation in dry, high-temperature environments. This oxidation produces a passive silicon oxide scale on the surface of the material. In moist, high-temperature environments containing water vapor, such as turbine engines, both oxidation and recession occur through the formation of a passive silicon oxide scale and the subsequent conversion of silicon oxide to gaseous silicon hydroxide. To prevent recession in moist, high-temperature environments, environmental barrier coatings (EBCs) are deposited on silicon carbide and silicon nitride materials.

[0005]

[0005] Currently, EBC materials are made from rare earth silicate compounds. These materials block water vapor and prevent it from reaching the silicon oxide scale on the silicon carbide or silicon nitride surface, thereby preventing recession. However, such materials cannot prevent oxygen penetration, which results in oxidation of the underlying substrate. Oxidation of the substrate produces a passive silicon oxide scale along with the release of carbonaceous or nitrous oxide gases. Carbonaceous oxide (i.e., CO, CO2) or nitrous oxide (i.e., NO, NO2, etc.) gases cannot escape through the dense EBC, and thus blisters can form, causing spalling of the EBC. The use of silicon bond coats has been the solution to the blister problem to date. The silicon bond coat provides a layer that oxidizes (forming a passive silicon oxide layer underneath the EBC) without releasing gaseous by-products.

[0006] A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in this specification, which makes reference to the accompanying drawings. [Brief description of the drawings]

[0007] [Figure 1] 1 is a cross-sectional schematic view of an exemplary coated part including a bond coat and an EBC thereon. [Diagram 2]

[0008] FIG. 1 is a side cross-sectional view of an exemplary bond coat formed from a matrix having a plurality of discrete particles, including first discrete particles and second discrete particles dispersed therein; [Diagram 3]

[0009] 1 is a schematic cross-sectional view of an exemplary gas turbine engine in accordance with various embodiments of the present subject matter. [Figure 4]

[0010] FIG. 1 is a flow chart diagram of an exemplary method of forming a coated component having a bond coat formed from a matrix having discrete particles dispersed therein. [Diagram 5]

[0011] 1 illustrates a cross-sectional view of an exemplary bond coat formed in accordance with embodiments described in more detail below. [Figure 6]

[0012] 1 illustrates a cross-sectional view of an exemplary bond coat formed in accordance with embodiments described in more detail below. [Figure 7]

[0013] 1 illustrates a cross-sectional view of an exemplary bond coat formed in accordance with embodiments described in more detail below. [Figure 8]

[0014] 1 illustrates a cross-sectional view of an exemplary bond coat formed in accordance with embodiments described in more detail below. [Figure 9]

[0015] 1 shows a cross-sectional view of a comparative bond coat formed in accordance with an embodiment described in more detail below. [Figure 10]

[0016] 3 shows a cross-sectional view of another comparative bond coat formed as described in more detail below. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008]

[0017] Repeat use of reference characters in the present specification and drawings is intended to represent same or analogous features or elements of the invention.

[0009] definition

[0018] As used herein, the terms "first," "second," and "third" may be used interchangeably to distinguish one component from another and are not intended to denote the position or importance of the individual components.

[0010]

[0019] Chemical elements are discussed in this disclosure using their common chemical abbreviations as commonly found in the periodic table of elements. For example, hydrogen is represented by its common chemical abbreviation H, helium is represented by its common chemical abbreviation He, and so on. As used herein, "RE" refers to a rare earth element or mixture of rare earth elements. More specifically, "RE" refers to the rare earth elements 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 mixtures thereof.

[0011]

[0020] As used herein, "alumina" refers to aluminum oxide in the form of Al2O3.

[0012]

[0021] As used herein, "silica" refers to silicon oxide in the form of SiO2.

[0013]

[0022] Conversely, "elemental silicon" refers to silicon that is free of alloying materials, except for incidental impurities. It is sometimes referred to in the art as "silicon metal." Elemental silicon has a melting point of approximately 1414°C.

[0014]

[0023] As used herein, the term "mullite" generally refers to a mineral containing alumina and silica. That is, mullite is a compound of alumina and silica with a ratio of alumina (Al2O3) to silica (SiO2) of about 3 to 2 (e.g., within 10 mole percent of 3 to 2 alumina to silica). However, a ratio of about 2 to 1 has also been reported for mullite (e.g., within 10 mole percent of 2 to 1 alumina to silica).

[0015]

[0024] As used herein, "transition metal" refers to 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).

[0016]

[0025] As used herein, the term "substantially free" is understood to mean completely free of said component or containing trace amounts of said component. A "trace amount" is a quantitative level of a chemical component that is barely detectable and provides no benefit to the functional or aesthetic properties of the subject composition. The term "substantially free" also encompasses complete absence.

[0017]

[0026] In this disclosure, when a layer is described as "on" or "over" another layer or substrate, it should be understood that the layers may be in direct contact with one another or have another layer or feature between them, unless expressly stated to the contrary. Thus, these terms are merely descriptive of the relative positions of the layers with respect to one another, and do not necessarily mean "above," as a relative position of above or below depends on the orientation of the device relative to the viewer.

[0018]

[0027] Reference will now be made in detail to the embodiments of the invention, one or more examples of which are illustrated in the drawings. The examples are provided by way of explanation of the invention, not as a limitation of the invention. Indeed, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope of the invention. For example, features illustrated or described as part of one embodiment can be used with another embodiment to yield a further embodiment. It is therefore intended that the present invention cover such modifications and variations as come within the scope of the appended claims and their equivalents.

[0019]

[0028] The presence of a silicon bond coat limits the upper temperature of operation of the EBC since silicon metal has a relatively low melting point of about 1414°C. Above these melting points, the silicon bond coat may delaminate from the underlying substrate, effectively removing the bond coat and the EBC thereon. Recently, high temperature EBCs have been contemplated that utilize bond coats containing silicon particles as oxygen getters.

[0020]

[0029] However, these high temperature EBCs have been shown to be weak in the intermediate temperature range. In particular, it is desirable for the bond coat to prevent both water and oxygen penetration into the underlying substrate at temperatures between 650°C and 1500°C. To prevent water penetration, it is desirable to minimize or eliminate any open porosity in the bond coat. Thus, it would be desirable to have an improved bond coat in an EBC that remains effective at lower and intermediate temperatures while achieving a higher operating temperature limit for the EBC.

[0021]

[0030] In principle, liquid phase sintering of a mullite layer can lead to a dense mullite layer. However, the residual liquid phase in this layer leads to high oxidant permeability paths in the mullite, which essentially negates the benefits of higher density. The methods and coatings described herein address proper composition selection, which can lead to densification of mullite via liquid phase sintering, but without incurring significant penalties in high and low temperature oxidation life. Thus, the methods and coatings described herein can prevent water penetration, without incurring significant penalties in high and low temperature oxidation life, by eliminating open porosity in the EBC through the formation of a dense mullite layer.

[0022]

[0031] The coated parts generally include a bond coat containing a matrix phase having a plurality of discrete particles dispersed therein, along with a method of its formation and use. Generally, the plurality of discrete particles includes an oxygen getter and a transition metal oxide. Without wishing to be bound by any particular theory, the presence of the transition metal oxide aids in densifying the mullite by liquid phase sintering, but does not incur a significant penalty in high and low temperature oxidation life. For example, the methods disclosed herein can result in the elimination of open porosity in the bond coat through the formation of 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) but does not result in a significant decrease in oxidation life.

[0023]

[0032] The mullite-containing bond coat, including discrete particles, in one particular embodiment, is generally disposed between a surface of a substrate and an environmental barrier coating (EBC) thereon. Referring to FIG. 1, an exemplary coated part 100 is shown formed from a substrate 102 having a surface 103 having a coating system 106 thereon. Generally, the coating system 106 includes a bond coat 104 on the substrate surface 103 and an EBC 108 on the bond coat 104. In the embodiment shown, the bond coat 104 is directly on the surface 103 without any layers in between.

[0024]

[0033] In the exemplary embodiment of FIG. 2, the bond coat 104 is shown having a matrix phase 112 having a plurality of discrete particles 110 dispersed therein. Generally, the plurality of discrete particles 110 includes an oxygen getter 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 getter and the transition metal oxide may form mixed particles. In the illustrated embodiment, the matrix phase 112 forms a continuous phase of the bond coat 104. Moreover, in the embodiment shown in FIG. 1, the matrix phase 112 extends through the thickness of the bond coat 104 and is directly bonded to the surface 103 of the substrate 102 and to the inner surface 107 of the EBC 108.

[0025]

[0034] Generally, the first discrete particles 111a of the plurality of discrete particles 110 include an oxygen getter configured to react with oxygen during use of the component to inhibit oxygen from reaching the underlying surface 103 of the substrate 102 and densify the coating during processing. The second discrete particles 111b of the bond coat discrete particles 110 include a transition metal oxide. In most embodiments, the oxygen getter and the transition metal oxide form different particles (i.e., the first discrete particles 111a and the second discrete particles 111b). However, in other embodiments, the oxygen getter and the transition metal oxide form a composite particle within the matrix phase 112.

[0026]

[0035] Transition metal oxides are generally called transition metal oxides (TM x O y , where TM is a transition metal and x, y are integers that balance the valence of the oxide). In one particular embodiment, the transition metal oxide is, in particular, Al2O3-SiO2-TM x O yIf it is close to Si in the phase diagram, it is resistant to chemical reduction to its metallic form (e.g., elemental transition metal). In general, any lanthanide oxide has the potential to be a liquid phase sintering aid, but Al2O3-SiO2-TM x O y The highest temperature eutectic compositions in the phase diagram are believed to be particularly suitable. For example, particularly suitable transition metal oxides may include, but are not limited to, Y2O3, Lu2O3, Sc2O3, TiO2, Ta2O5, La2O3, CeO2, or mixtures thereof.

[0027]

[0036] The transition metal oxide may be in the form of a simple oxide or, alternatively, may be in the form of an aluminate-transition metal oxide complex or a silicate-transition metal oxide complex. In one particular embodiment, for example, aluminum oxide and a transition metal oxide (e.g., Al2O3-TM x O y A transition metal oxide can be included in the aluminate formed from mullite (AlO) to form an aluminate-transition metal oxide composite. In such an embodiment, the additional aluminum oxide can be sintered with the mullite to form an aluminum-rich mullite composition. For example, excess Al2O3 can also form an aluminum oxide (e.g., Al2O3) phase in the mullite. Without wishing to be bound by any particular theory, it is believed that having excess aluminum oxide can help slow the initial oxidation of the oxygen getter, particularly the bond coat and the EBC layer thereon. Additionally, it is believed that silicon oxide and transition metal oxide composited together can lead to improved reaction kinetics.

[0028]

[0037] The oxygen getter and transition metal oxide may be included in the bond coat in relative amounts sufficient to prevent oxygen from reaching the underlying surface, to keep the bond coat relatively low in porosity, and / or to maintain the structural integrity of the bond coat even at relatively high temperatures. In certain embodiments, the oxygen getter may be included in the bond coat at 1 wt. % to 30 wt. %, such as 1 wt. % to 10 wt. %. In certain embodiments, the transition metal oxide may be included in the bond coat at 0.1 wt. % to 10 wt. %, such as 1 wt. % to 5 wt. %. For example, the transition metal oxide may be included in the bond coat in a range of 0.1 mol. % to 10 mol. %, such as 0.5 mol. % to 5 mol. % of the matrix material.

[0029]

[0038] In one embodiment, the oxygen getter comprises silicon, such as elemental silicon. For example, the oxygen getter can consist essentially of silicon (upon formation of the bond coat), such that at least 95% by weight of the oxygen getter is silicon (before exposure to any oxygen), e.g., such that at least 99% by weight of the oxygen getter is silicon.

[0030]

[0039] In one particular embodiment, the bond coat 104 may be formed from a mixture of transition metal oxides and elemental silicon (both as discrete particles 110) contained within a matrix phase 112. As described in more detail below, the elemental silicon in the mullite remains contained within the matrix phase and may melt during operation of the coated component while maintaining the functionality of the bond coat 104. Such functions of the bond coat 104 include, but are not limited to, bonding the substrate to the EBC thereon and gettering oxygen without outgassing to prevent oxidation of the underlying substrate that would otherwise result in gaseous by-products. Thus, liquid discrete particles may be utilized within the bond coat 104 during operation of the coated component (e.g., in a gas turbine engine). The bond coat 104 continues to function beyond the melting point of the discrete particles, allowing the coated component to operate at temperatures above the melting point of the discrete particles.

[0031]

[0040] Although silicon does not oxidize to form gases such as CO from SiC, it does form silicon hydroxide gas species when in contact with water vapor. However, the partial pressures of the silicon hydroxide gas species are low enough that they do not significantly form bubbles. Furthermore, these partial pressures inhibit recession unless there are interconnected pores at the outer gas surface. The density of the mullite matrix and the hermeticity of the upper layer of the EBC can be controlled to minimize the formation of silicon hydroxide.

[0032]

[0041] In one embodiment, the discrete particles are generally coarse and have a sufficient size that their oxidation reaction occurs relatively slowly throughout the thickness of the bond coat. Without wishing to be bound by a particular theory, it is believed that oxidation occurs only on a thin surface layer of the relatively coarse particles, effectively slowing down the oxidation of the discrete particles compared to the finer particles. Thus, the presence of the relatively coarse particles can create a more manageable stress state compared to the finer particles, thus resulting in less cracking tendency. Furthermore, the oxidation of the relatively coarse particles can create a diffuse reaction zone within the thickness of the bond coat, instead of the sharp reaction front seen with the smaller particles. Furthermore, the discrete particles undergo oxidation or evaporation during the manufacturing process of the coating. The coarse particles provide the advantage of slowing down such degradation, and thus may help maintain a desired ratio of particles in the bond coat.

[0033]

[0042] As mentioned above, the plurality of discrete particles have a relatively large size (i.e., coarse grains) so that the oxidation reaction of the oxygen getter occurs relatively slowly throughout the thickness of the bond coat. However, if the size and / or content of the discrete particles 110 are too large, the discrete particles may form a continuous phase in use at temperatures at which the oxygen getter liquefies (e.g., temperatures above 1414° C. if silicon is included). Too much continuous phase (formed by too large discrete particles that liquefy) may result in spalling of the coating.

[0034]

[0043] For example, the plurality of discrete particles may have 50% or more of their volume (e.g., 75% or more of their volume) formed from particles having an average size between 10 μm and 100 μm. In one embodiment, the plurality of discrete particles may have 50% or more of their volume (e.g., 75% or more of their volume) formed from particles having an average size between 20 μm and 75 μm. In one particular embodiment, the plurality of discrete particles may have 50% or more of their volume (e.g., 75% or more of their volume) formed from particles having an average size between 30 μm and 50 μm. Thus, without wishing to be bound by any particular theory, it is believed that the presence of these relatively large particles slows down the oxidation reaction, forming a diffusion reaction zone, reducing expansion stresses and inhibiting cracking.

[0035]

[0044] Regardless of the configuration of the bond coat 104, upon melting of the oxygen getter, the discrete particles 110 are contained within a matrix phase 112 between the surface 103 of the substrate 102 and the inner surface 107 of the environmental barrier coating 108. That is, the matrix phase 112 may form a three-dimensional network that spans the thickness of the bond coat 104 and is bonded to the surface 103 of the substrate 102 and to the inner surface 107 of the environmental barrier coating 108. In this manner, the matrix phase 112 acts in conjunction with the surface 103 of the substrate 102 and the environmental barrier coating 108 to contain the molten oxygen getter therein while maintaining the integrity of the bond coat 104 without delaminating from the surface 103 of the substrate 102.

[0036]

[0045] Thus, the matrix phase 112 is included in the bond coat 104 in an amount that provides structural integrity to the bond coat 104, while the oxygen getter of the discrete particles 110 is melted at an operating temperature that exceeds the melting point of elemental silicon (i.e., about 1414° C.) if the oxygen getter is silicon, while incorporating a sufficient amount of the oxygen getter therein. The matrix phase 112 also functions to limit the diffusion of an oxidizing agent, i.e., oxygen or water vapor, to reach the discrete particles 110. In an embodiment, the matrix phase can define at least 60% by volume of the bond coat 104 (e.g., at least 60% by volume of the bond coat 104 can include mullite). In a particular embodiment, the bond coat 104 can include 60% to 98% by volume of the matrix phase (e.g., mullite), such as 65% to 96% by volume of the matrix phase (e.g., mullite), such as 75% to 95% by volume of the matrix phase (e.g., mullite).

[0037]

[0046] Conversely, 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 prevent oxygen from reaching the underlying substrate 102. In one particular embodiment, the oxygen getter may be formed of silicon metal (i.e., elemental silicon), a silicon alloy (e.g., a silicon eutectic alloy), a silicide, or a mixture thereof. Thus, the oxygen getter may melt when the bond coat 104 reaches a temperature of about 1400°C to about 2550°C, depending on the composition of the oxygen getter. In some embodiments, the matrix phase 112 includes mullite and has a melting point of about 1825°C to 1890°C. Under some circumstances, the temperature of the bond coat 104 may be higher than the melting point of the oxygen getter and lower than the melting point of the matrix phase 112, such that the oxygen getter melts. For example, the oxygen getter may have a melting point of about 1414°C (i.e., the melting point of elemental silicon) to about 1485°C. In certain embodiments, the oxygen getter may be formed from a silicon material that is melted at bond coat temperatures of 1415°C, 1450°C, 1550°C, and / or 1600°C.

[0038]

[0047] For example, the bond coat 104 may, in certain embodiments, include 2% to 40% by volume of the discrete particles 110 (i.e., the total volume of the mixture of oxygen getter and transition metal oxide), such as 4% to 35% by volume of the discrete particles 110 (e.g., 5% to 25% by volume of the discrete particles 110).

[0039]

[0048] In certain embodiments, a silicide having a melting point of about 1900° C. or less (e.g., about 1400° C. to about 1900° C.) may be present in the discrete particles 110 as an oxygen getter. Determining the melting point of a particular silicide can be readily accomplished using a Si phase diagram.

[0040]

[0049] In certain embodiments, the oxygen getter in the discrete particles may have a minimal thermal expansion coefficient mismatch (e.g., about 2-3 ppm per °C or less) with the substrate and mullite to avoid matrix cracking. However, one skilled in the art knows that a larger expansion coefficient mismatch can be accommodated by decreasing the volume fraction of the getter phase. In another particular embodiment, the oxygen getter should have a minimal volume increase upon oxidation (e.g., 150% or less, preferably 100% or less, more preferably a volume decrease upon oxidation rather than a volume expansion) to reduce stress in the mullite layer and its cracks. Many embodiments of the discrete particles are possible that meet the expansion coefficient mismatch and volume change upon oxidation requirements. In one embodiment, the oxygen getter includes elemental silicon and may be pure elemental silicon. In another embodiment, the oxygen getter includes silicon alloys and / or silicides. In embodiments where the oxygen getter includes elemental silicon, the bond coat may be referred to as a "mullite / Si bond coat." Silicon oxidation produces a volume expansion of about 115% to about 130% if it forms amorphous silica, and about 85% if it forms crystalline silica, but the oxidation products are always initially amorphous and may subsequently become crystalline over time.

[0041]

[0050] Other embodiments of oxygen getters include, but are not limited to, nickel, cobalt, chromium, or mixtures thereof. These oxygen getters may be used in certain embodiments with silicon, silicon alloys, and / or silicides. For example, nickel has a much larger expansion mismatch with the substrate and mullite (nearly 8 ppm per °C). Thus, the maximum volume fraction of nickel that can be tolerated would be lower than that of silicon, which has a mismatch of less than 1 ppm / °C. However, nickel has a volume expansion of about 65% upon oxidation, compared to about 115% to about 130% for silicon, which converts to amorphous silica. On the other hand, chromium has a smaller expansion mismatch with the substrate and mullite than nickel. It also has a higher melting point (1907°C) compared to silicon (1410°C) and nickel (1455°C).

[0042]

[0051] The matrix phase 112 can include oxide materials, particularly oxide materials having a melting point higher than that of the oxygen getter. Additionally, the matrix phase 112 can include oxide materials that generally do not react with the oxygen getter of the discrete particles 110, even at high operating temperatures. In one particular embodiment, the matrix phase 112 is formed from crystallized mullite, which has a melting point higher than that of the oxygen getter. In a particular embodiment, mullite has a melting point of about 1825° C. to 1890° C. and generally does not react with the oxygen getter and / or the transition metal oxide of the discrete particles 110.

[0043]

[0052] In one embodiment, the matrix phase 112 can include mullite with excess 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 about 2:1 to about 2.25:1. In another embodiment, the matrix phase 112 can include mullite containing excess silica.

[0044]

[0053] Mullite generally has a relatively slow diffusion rate for oxygen at all temperatures of interest, even up to 1650°C (e.g., 1200°C-1650°C). At temperatures above 1200°C, the only other crystalline oxide with a lower oxygen diffusion rate than mullite is believed to be alumina, which has a very high coefficient of expansion compared to the substrate and cannot be deposited as a dense coating without spalling. Mullite has a similar coefficient of thermal expansion ("CTE") to the SiC CMC substrate 102, but the CTE of mullite does not match SiC exactly. If the bond coat 104 is too thick, even a slight mismatch in the CTE of mullite and SiC can cause thermal expansion related problems, 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 CTE mismatch related problems after repeated exposure to operating temperatures. On the other hand, a bond coat 104 having a maximum thickness of 15 mils or less, such as 1 mil to 15 mils (i.e., 381 μm or less, e.g., 25.4 μm to 381 μm), is believed to withstand such operating temperatures without significant issues due to CTE mismatch. In one particular embodiment, the bond coat 104 has a maximum thickness of 10 mils, such as 3 mils to 10 mils (i.e., 127 μm, e.g., 76.2 μm to 254 μm).

[0045]

[0054] As discussed above, the combination of an oxygen getter and a transition metal oxide in a 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.

[0046]

[0055] In one particular embodiment, the substrate 102 is formed from a ceramic matrix composite ("CMC"). As used herein, 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. Generally, 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-based materials (e.g., silicon carbide, silicon nitride, or mixtures thereof), oxide ceramics (e.g., silicon oxycarbide, silicon oxynitride, aluminum oxide (Al2O3), silicon dioxide (SiO2), aluminosilicates, 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.

[0047]

[0056] Some examples of reinforcing fibers of a CMC can include, but are not limited to, a non-oxide silicon-based material (e.g., silicon carbide, silicon nitride, or mixtures thereof), a non-oxide carbon-based material (e.g., carbon), an oxide ceramic (e.g., silicon oxycarbide, silicon oxynitride, aluminum oxide (Al2O3), silicon dioxide (SiO2), an aluminosilicate such as mullite, or mixtures thereof), or a mixture thereof.

[0048]

[0057] In general, a particular CMC may be referred to as a fiber type / matrix type combination, such as C / SiC for carbon fiber reinforced silicon carbide, SiC / SiC for silicon carbide fiber reinforced silicon carbide, SiC / SiN for silicon carbide fiber reinforced silicon nitride, or SiC / SiC-SiN for silicon carbide fiber reinforced silicon carbide / silicon nitride matrix mixture. In other examples, CMCs may be composed of a matrix and reinforcing fibers that include oxide-based materials such as aluminum oxide (Al2O3), silicon dioxide (SiO2), aluminosilicates, and mixtures thereof. Aluminosilicates can include crystalline materials such as mullite (3Al2O3·2SiO2), as well as glassy aluminosilicates.

[0049]

[0058] In certain embodiments, the reinforcing fibers may be bundled and / or coated before being included in the matrix. For example, the fiber bundles may be formed as a reinforcing tape, such as a unidirectional reinforcing tape. A plurality of tapes may be laminated together to form a preform part. The fiber bundles may be impregnated with a slurry composition before forming the preform or after forming the preform. The preform may then undergo a heat treatment, such as curing or burnout, to produce high char residues in the preform, and a subsequent chemical treatment, such as melt infiltration with silicon, to arrive at a part formed from the CMC material with a desired chemical composition.

[0050]

[0059] Such materials, along with certain monolithic ceramics (i.e., ceramic materials without reinforcing materials), are particularly suited for high temperature applications. Moreover, these ceramic materials are lightweight compared to superalloys, yet can provide strength and durability to components made therefrom. Thus, such materials are currently being considered for many gas turbine components used in the hotter portions of gas turbine engines, such as airfoils (e.g., turbines and blades), combustors, shrouds, and other similar components, which would benefit from the lighter weight, higher temperature capabilities that these materials can provide.

[0051]

[0060] As used herein, environmental barrier coating or "EBC" refers to a coating system that includes one or more layers of ceramic materials, each of which provides specific or multi-functional protection to the underlying CMC. EBCs generally include multiple layers, such as a rare earth silicate coating (e.g., a rare earth disilicate, such as slurry or APS-deposited ytterbium yttrium disilicate (YbYDS)), an alkaline earth aluminosilicate (e.g., including barium-strontium-aluminum silicate (BSAS), such as having a range of BaO, SrO, Al2O3, and / or SiO2 compositions), a hermetic layer (e.g., a rare earth disilicate), and / or an outer coating (e.g., including a rare earth monosilicate, such as slurry or APS-deposited yttrium monosilicate (YMS)). One or more layers may be doped as desired, and the EBC may also be coated with an abradable coating.

[0052]

[0061] As discussed above, the bond coat 104 can be used with the EBC 108 to form a coated component 100 having a higher operating temperature compared to using only a silicon bond coat (without a matrix phase). The EBC 108 can include any combination of one or more layers 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 aluminosilicate (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.

[0053]

[0062] The EBC 108 may be formed from multiple individual layers 114. In the embodiment shown, the EBC 108 includes a hermetic layer 116 disposed directly on the bond coat 104 to contain the oxygen getters of the discrete particles 110 within the bond coat 104 upon melting. In one embodiment, the hermetic layer is 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). The oxygen getters of the discrete particles 110 are reactive with oxygen (e.g., form silicon oxide), so that minimal gaseous oxides (e.g., carbon oxides) are produced upon exposure of the component 100 to oxygen at operating temperatures. Thus, a gas escape layer through the bond coat 104 is not necessary, and the hermetic layer may be included within the EBC 108. It is also desirable to have a hermetic layer to prevent ingress of water vapor into the bond coat 104. In one embodiment, the gas-tight layer 116 may be disposed directly on the bond coat 104 , but may also be disposed elsewhere within the EBC 108 .

[0054]

[0063] The coated component 100 is particularly suitable for use as a component found in high temperature environments, such as components present in gas turbine engines, such as combustor components, turbine blades, shrouds, nozzles, heat shields, and vanes. In particular, the coated component 100 may be a CMC component located in a hot gas path of a gas turbine, whereby the coating system 106 forms an environmental barrier against the underlying substrate 102 to protect the component 100 within the gas turbine when exposed 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 is substantially unaffected by these operating temperatures. Thus, the bond coat 104 can withstand exposure to operating temperatures of about 1475°C to about 1650°C.

[0055]

[0064] FIG. 3 is a schematic cross-sectional view of a gas turbine engine according to an exemplary embodiment of the present disclosure. More specifically, in the embodiment of FIG. 3, the gas turbine engine is a high bypass turbofan jet engine 10, referred to herein as a "turbofan engine 10." As shown in FIG. 3, the turbofan engine 10 defines an axial direction A (extending parallel to a longitudinal axis 12 provided for reference) and a radial direction R. In general, the turbofan engine 10 includes a fan section 14 and a core turbine engine 16 disposed downstream of the fan section 14. Although described below with reference to the turbofan engine 10, the present disclosure is applicable to turbomachinery in general, including turbojet, turboprop and turboshaft gas turbine engines, including industrial and marine gas turbine engines and auxiliary power units. It is also applicable to other high temperature applications that include water vapor in the gas phase, such as those resulting from the combustion of hydrocarbon fuels.

[0056]

[0065] The illustrated exemplary core turbine engine 16 generally includes a substantially tubular outer casing 18 defining an annular inlet 20. The casing 18 houses, 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.

[0057]

[0066] In the illustrated embodiment, the fan section 14 includes a variable pitch fan 38 having a plurality of fan blades 40 spaced apart and coupled to a disk 42. As shown, the fan blades 40 extend generally outwardly from the disk 42 along a radial direction R. Each fan blade 40 is rotatable relative to the disk 42 about a pitch axis P by the fan blades 40 being operatively coupled to a suitable actuating member 44 configured to collectively vary the pitch of the fan blades 40 in unison. The fan blades 40, disk 42, and actuating member 44 are rotatable together about the longitudinal axis 12 by the LP shaft 36 across 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 fan rotational speed.

[0058]

[0067] 3, the disk 42 is covered by a rotatable front nacelle 48 that is aerodynamically contoured to facilitate airflow through the plurality of fan blades 40. Additionally, the exemplary fan section 14 includes an annular fan casing or outer nacelle 50 that circumferentially surrounds the fan 38 and / or at least a portion of the core turbine engine 16. It should be appreciated that the nacelle 50 may be configured to be supported relative to the core turbine engine 16 by a plurality of circumferentially spaced outlet guide vanes 52. Additionally, a downstream section 54 of the nacelle 50 may extend over an outer portion of the core turbine engine 16 to define a bypass airflow passage 56 therebetween.

[0059]

[0068] During operation of the turbofan engine 10, a volume of air 58 enters the turbofan engine 10 through an associated inlet 60 in 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, indicated by arrow 62, is directed or routed to the bypass air passage 56, and a second portion of the air, indicated by arrow 64, is directed or routed to the LP compressor 22. The ratio between the first portion of air 62 and the second portion of air 64 is commonly known as the bypass ratio. The pressure of the second portion of air 64 then increases as it is routed through the high pressure (HP) compressor 24 and into the combustion section 26, where it is mixed with fuel and combusted to provide combustion gases 66.

[0060]

[0069] The combustion gases 66 are routed through the HP turbine 28 where a portion of the thermal energy and / or kinetic energy from the combustion gases 66 is extracted via successive stages of HP turbine vanes 68 coupled to the outer casing 18 and HP turbine rotor blades 70 coupled to the HP spool or shaft 34, thereby rotating the HP spool or shaft 34 and thereby supporting the operation of the HP compressor 24. The combustion gases 66 are then routed through the LP turbine 30 where a second portion of the thermal energy and kinetic energy is extracted from the combustion gases 66 via successive stages of LP turbine vanes 72 connected to the outer casing 18 and LP turbine rotor blades 74 coupled to the LP spool or shaft 36, thereby rotating the LP spool or shaft 36 and thereby supporting the operation of the LP compressor 22 and / or the rotation of the fan 38.

[0061]

[0070] The combustion gases 66 then flow through the jet exhaust nozzle section 32 of the core turbine engine 16 to provide thrust. At the same time, the pressure of the first portion of the air 62 is substantially increased as the first portion of the air 62 is channeled through the bypass air passage 56 before being exhausted from a fan nozzle exhaust section 76 of the turbofan engine 10, also providing 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 channeling the combustion gases 66 through the core turbine engine 16.

[0062]

[0071] Methods for coating ceramic components are also generally provided. For example, FIG. 4 shows a diagram of an exemplary method 400 of forming a coating system on a surface of a substrate. At 402, a bond coat is formed on a surface of a substrate to include discrete particles contained within a matrix phase, as described above with respect to the 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, where a liquid suspension of the desired chemistry is used in the air plasma spraying. In yet another embodiment, the coating is formed by low pressure plasma spraying. In yet another embodiment, one or more coating layers may be formed by a slurry coating process followed by sintering of the layers. Different coating layers may be formed by one or more of these processes.

[0063]

[0072] An environmental barrier coating (EBC) is formed on the bond coat at 404. As described above, the discrete particles, when fused, are contained within a matrix phase between the surface of the substrate and the inner surface of the environmental barrier coating.

[0064] Working Example

[0073] Exemplary bond coat materials were prepared with mixtures of oxygen getters and transition metal oxides dispersed within a continuous mullite phase, and comparative bond coat materials were prepared without the transition metal oxide.

[0065]

[0074] FIG. 5 shows a photograph of a pellet including an exemplary bond coat material after thermal testing. The pellet including the exemplary bond coat material was formed from 75.5 wt. % mullite as a matrix material, 12.7 wt. % Al2O3 to make the mullite aluminum rich, 9.6 wt. % elemental silicon as an oxygen getter, and 2.1 wt. % Lu2O3 as a transition metal oxide. The exemplary bond coat material was formed by cold pressing a powder mixture of mullite, Al2O3, silicon, and Lu2O3 into a pellet, followed by vacuum sintering. This bond coat material was not a coating, but served as an exemplary bond coat material. The pellet was then subjected to a heat test at temperatures of 1480°C to 1540°C in air for 10 hours to determine whether porosity was formed within the layer. As shown, the porosity within the pellet is substantially eliminated, even after thermal testing.

[0066]

[0075] FIG. 6 shows a photograph of a pellet containing an exemplary bond coat material after thermal testing. The pellet with the exemplary bond coat material was formed from 76.6 wt. % mullite as a matrix material, 12.9 wt. % Al2O3 to make the mullite aluminum rich, 9.8 wt. % elemental silicon as an oxygen getter, and 0.7 wt. % Sc2O3 as a transition metal oxide. The exemplary bond coat material was formed by cold pressing a powder mixture of mullite, Al2O3, silicon, and Sc2O3 into a pellet, followed by vacuum sintering. This bond coat material was not a coating, but served as an exemplary bond coat material. The pellet was then subjected to a heating test at temperatures of 1480°C to 1540°C in air for 10 hours to determine whether porosity formed within the layer. As shown, the porosity within the pellet is extremely small, even after thermal testing.

[0067]

[0076] FIG. 7 shows a photograph of a pellet containing an exemplary bond coat material after thermal testing. The pellet with the exemplary bond coat material was formed from 76.5 wt. % mullite as a matrix material, 12.8 wt. % Al2O3 to make the mullite aluminum rich, 9.8 wt. % elemental silicon as an oxygen getter, and 0.9 wt. % TiO2 as a transition metal oxide. The exemplary bond coat material was formed by cold pressing a powder mixture of mullite, Al2O3, silicon, and TiO2 into a pellet, followed by vacuum sintering. This bond coat material was not a coating, but served as an exemplary bond coat material. The pellet was then subjected to a heating test at temperatures of 1480°C to 1540°C in air for 10 hours to determine if porosity formed within the layer. As shown, the porosity within the pellet is extremely small, even after thermal testing.

[0068]

[0077] FIG. 8 shows a cross-sectional view of an exemplary bond coat material after thermal testing. The exemplary bond coat material was formed by solution plasma spraying of 85% by volume mullite as a matrix material, 10% by weight Al2O3 (relative to the total weight of mullite and silicon) to make the mullite aluminum rich, 15% by volume elemental silicon as an oxygen getter, and 3.2% by weight Lu2Si2O7 (relative to the total weight of mullite and silicon) as a transition metal oxide. The solid fraction of the solution plasma spray was as follows: 77% by weight mullite, 11% by weight Si, 9% by weight Al2O3, and 3% by weight Lu2Si2O7. This coating was then subjected to a thermal test at a temperature of 1540° C. for 10 hours in air to determine whether porosity was formed within the layer. As shown, the porosity within the bond coat was substantially eliminated, even after thermal testing.

[0069]

[0078] FIG. 9 shows a photograph of a pellet containing the comparative bond coat material without any transition metal oxides present after thermal testing. The pellet containing the comparative bond coat material was formed from 77.1 wt. % mullite as the matrix material, 13 wt. % Al2O3 to make the mullite aluminum rich, and 9.9 wt. % elemental silicon as an oxygen getter. The comparative bond coat material was formed by cold pressing a powder mixture of mullite, Al2O3, and silicon into a pellet followed by vacuum sintering. The comparative bond coat material was formed in the same manner as the pellets described above with respect to FIGS. 5, 6, and 7, except that no transition metal oxides were present. The pellets were then subjected to a heat test at temperatures between 1480° C. and 1540° C. for 10 hours in air to determine if porosity formed within the layer. As shown in FIG. 9, there is significant open porosity within the comparative pellets after thermal testing.

[0070]

[0079] FIG. 10 shows a cross-sectional view of the comparative bond coat material after thermal testing. The comparative bond coat material was formed by solution plasma spraying of 85% by volume mullite as the matrix material, 10% by weight Al2O3 (relative to the total weight of mullite and silicon) to make the mullite aluminum rich, and 15% by volume elemental silicon as an oxygen getter. The solution plasma spray solid fraction was 79% by weight mullite, 12% by weight Si, and 9% by weight Al2O3. This comparative bond coat was formed in the same manner as the coating described above with respect to FIG. 8, except that no transition metal oxide was present. This coating was then subjected to a thermal test at a temperature of 1540° C. for 10 hours in air to determine if porosity formed within the layer. As shown, the porosity within the bond coat was much greater than that shown in the exemplary bond coat of FIG. 8 after thermal testing.

[0071]

[0080] Embodiments of the present disclosure prevent water penetration by eliminating open porosity in EBC through the formation of a dense mullite layer, without incurring significant penalties in high and low temperature oxidation life.

[0072]

[0081] Further aspects of the invention are provided by the subject matter of the following clauses.

[0073]

[0082] 1. 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 within 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.

[0074]

[0083] 2. The coated component of any preceding claim, wherein the transition metal oxide comprises Y2O3, Lu2O3, Sc2O3, TiO2, Ta2O5, La2O3, CeO2, or mixtures thereof.

[0075]

[0084] 13. The coated component of any preceding claim, wherein the bond coat comprises 0.1% to 10% by weight of the transition metal oxide.

[0076]

[0085] 13. The coated component of any preceding claim, wherein the bond coat has a porosity of less than 15%.

[0077]

[0086] 13. The coated component of any preceding claim, wherein the oxygen getter forms first discrete particles within the plurality of discrete particles and the transition metal oxide forms second discrete particles within the plurality of discrete particles.

[0078]

[0087] 13. The coated component of any preceding claim, wherein the oxygen getter comprises elemental silicon, a silicon alloy, a silicide, or a mixture thereof.

[0079]

[0088] 13. The coated component of any preceding claim, wherein the oxygen getter comprises elemental silicon.

[0080]

[0089] 13. The coated component of any preceding claim, wherein the bond coat comprises 1% to 30% by weight of an oxygen getter.

[0081]

[0090] 13. The coated component of any preceding paragraph, wherein the matrix phase is a continuous phase, the matrix phase extending through the bond coat and directly bonded to a surface of the substrate and to an inner surface of the environmental barrier coating.

[0082]

[0091] 13. The coated component of any preceding claim, wherein the matrix phase defines 60% to 98% by volume of the bond coat.

[0083]

[0092] 13. The coated component of any preceding paragraph, wherein the matrix phase defines 65% to 96% by volume of the bond coat.

[0084]

[0093] 13. The coated component of any preceding claim, wherein the matrix phase defines 75% to 95% by volume of the bond coat.

[0085]

[0094] 7. The coated component of any preceding claim, wherein the matrix phase consists essentially of mullite.

[0086]

[0095] 13. The coated component of any preceding claim, wherein the environmental barrier coating comprises a plurality of layers, and at least one of the layers of the environmental barrier coating comprises a hermetic layer.

[0087]

[0096] 13. The coated component of any preceding claim, wherein the hermetic layer is adjacent the bond coat such that the hermetic layer defines an inner surface of the environmental barrier coating.

[0088]

[0097] 13. The coated component of any preceding claim, wherein the bond coat is configured to withstand exposure to operating temperatures of 1475°C to 1650°C.

[0089]

[0098] The coated component of any preceding paragraph, wherein the environmental barrier coating comprises a hafnia layer, an alumina layer, or both.

[0090]

[0099] 13. The coated component of any preceding paragraph, wherein the environmental barrier coating comprises a rare earth disilicate layer, a rare earth monosilicate layer, or both.

[0091]

[0100] A method for forming the coated part of the preceding paragraph.

[0092]

[0101] 1. A method of forming a coated component, the method comprising: forming 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 forming an environmental barrier coating on the bond coat such that the plurality of discrete particles, when melted, are contained within the matrix phase between the surface of the substrate and an inner surface of the environmental barrier coating.

[0093]

[0102] 2. The method of any preceding claim, wherein the transition metal oxide comprises Y2O3, Lu2O3, Sc2O3, TiO2, Ta2O5, La2O3, CeO2, or mixtures thereof.

[0094]

[0103] This written description uses examples to disclose the invention, including the best mode, and also to enable those skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they contain structural elements that do not differ from the literal language of the claims, or if they contain equivalent structural elements that are not substantially different from the literal language of the claims.

[0095]

[0104] Further aspects of the invention are provided by the subject matter of the following clauses.

[0096]

[0105] 1. A coated part comprising: a ceramic matrix composite substrate comprising silicon carbide and having a surface; a bond coat on the surface of the ceramic matrix composite substrate, the bond coat comprising a plurality of discrete particles dispersed within a matrix phase, the plurality of discrete particles comprising an oxygen getter and a transition metal oxide, and the matrix phase comprising mullite; and an environmental barrier coating on the bond coat.

[0097]

[0106] 2. The coated component of any preceding paragraph, wherein the transition metal oxide comprises Y2O3, Lu2O3, Sc2O3, TiO2, Ta2O5, La2O3, CeO2, or mixtures thereof.

[0098]

[0107] 3. The coated component of any preceding claim, wherein the bond coat comprises 0.1% to 10% by weight of the transition metal oxide.

[0099]

[0108] 4. The coated component of any preceding paragraph, wherein the bond coat has a porosity of less than 15%.

[0100]

[0109] 5. The coated component of any preceding claim, wherein the oxygen getter forms first discrete particles within the plurality of discrete particles and the transition metal oxide forms second discrete particles within the plurality of discrete particles.

[0101]

[0110] 6. The coated component of any preceding paragraph, wherein the oxygen getter comprises elemental silicon, a silicon alloy, a silicide, or a mixture thereof.

[0102]

[0111] 7. The coated component of any preceding paragraph, wherein the oxygen getter comprises elemental silicon.

[0103]

[0112] 8. The coated component of any preceding paragraph, wherein the bond coat comprises 1% to 30% by weight of an oxygen getter.

[0104]

[0113] 9. The coated component of any preceding paragraph, wherein the matrix phase is a continuous phase, the matrix phase extending through the bond coat and directly bonded to a surface of the ceramic matrix composite substrate and to an inner surface of the environmental barrier coating.

[0105]

[0114] 10. The coated component of any preceding paragraph, wherein the matrix phase defines 60% to 98% by volume of the bond coat.

[0106]

[0115] 11. The coated component of any preceding paragraph, wherein the matrix phase defines 65% to 96% by volume of the bond coat.

[0107]

[0116] 12. The coated component of any preceding paragraph, wherein the matrix phase defines 75% to 95% by volume of the bond coat.

[0108]

[0117] 13. The coated component of any preceding paragraph, wherein the matrix phase consists essentially of mullite.

[0109]

[0118] 14. The coated component of any preceding paragraph, wherein the environmental barrier coating comprises a plurality of layers, and at least one of the layers of the environmental barrier coating comprises an airtight layer.

[0110]

[0119] 15. The coated component of any preceding paragraph, wherein the hermetic layer is adjacent to the bond coat such that the hermetic layer defines an inner surface of the environmental barrier coating.

[0111]

[0120] 16. The coated component of any preceding paragraph, wherein the bond coat is configured to withstand exposure to operating temperatures of 1475°C to 1650°C.

[0112]

[0121] 17. The coated component of any preceding paragraph, wherein the environmental barrier coating comprises a hafnia layer, an alumina layer, or both.

[0113]

[0122] 18. The coated component of any preceding paragraph, wherein the environmental barrier coating comprises a rare earth disilicate layer, a rare earth monosilicate layer, or both.

[0114]

[0123] 19. A method of forming a coated part, 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, the matrix phase comprising mullite; and forming an environmental barrier coating on the bond coat, the plurality of discrete particles, when melted, are contained within a matrix phase between the surface of the substrate and an inner surface of the environmental barrier coating.

[0115]

[0124] 20. The method of any preceding claim, wherein the transition metal oxide comprises Y2O3, Lu2O3, Sc2O3, TiO2, Ta2O5, La2O3, CeO2, or a mixture thereof.

Claims

1. A coated part (100) comprising: a ceramic matrix composite substrate (102) comprising silicon carbide and having a surface (103); a bond coat (104) on the surface (103) of the ceramic matrix composite substrate (102), the bond coat (104) comprising a plurality of discrete particles (110) dispersed within a matrix phase (112), the plurality of discrete particles (110) comprising an oxygen getter and a transition metal oxide, and the matrix phase (112) comprising mullite; an environmental barrier coating (108) on said bond coat (104); Including, The oxygen getter forms first discrete particles (111a) within the plurality of discrete particles (110), and the transition metal oxide forms second discrete particles (111b) within the plurality of discrete particles (110).

2. The transition metal oxide is Y ２ O ３ , Lu ２ O ３ , Sc ２ O ３ , TiO ２ , Ta ２ O ５ , La ２ O ３ , CeO ２ 10. The coated component (100) of claim 1, comprising:

3. The coated component (100) of any one of the preceding claims, wherein the bond coat (104) comprises between 0.1% and 10% by weight of the transition metal oxide.

4. The coated component (100) of claim 1, wherein the bond coat (104) has a porosity of less than 15%.

5. The coated component (100) of claim 1, wherein the oxygen getter comprises elemental silicon, a silicon alloy, a silicide, or a mixture thereof.

6. The coated component (100) of claim 1, wherein the oxygen getter comprises elemental silicon.

7. The coated component (100) of any preceding claim, wherein the bond coat (104) comprises between 1% and 30% by weight of an oxygen getter.

8. 2. The coated component (100) of claim 1, wherein the matrix phase (112) is a continuous phase, the matrix phase (112) extending through the bond coat (104) and directly bonded to a surface (103) of the ceramic matrix composite substrate (102) and to an inner surface (103) of the environmental barrier coating (108).

9. The coated component (100) of any preceding claim, wherein the matrix phase (112) defines between 60% and 98% by volume of the bond coat (104).

10. The coated component (100) of claim 1, wherein the matrix phase (112) consists essentially of mullite.

11. The coated component (100) of claim 1, wherein the environmental barrier coating (108) comprises a plurality of layers (114), and at least one of the layers (114) of the environmental barrier coating (108) comprises a hermetic layer (116).

12. The coated component (100) of claim 11, wherein the hermetic layer is adjacent to the bond coat (104) such that the hermetic layer defines an inner surface (103) of the environmental barrier coating (108).

13. The coated component (100) of claim 1, wherein the environmental barrier coating (108) comprises at least one of a hafnia layer, an alumina layer, a rare earth disilicate layer, and a rare earth monosilicate layer.

14. A method of forming a coated part (100) comprising: forming a bond coat (104) on a surface (103) of a substrate (102), the bond coat (104) comprising a plurality of discrete particles (110) dispersed within a matrix phase (112), the plurality of discrete particles (110) comprising an oxygen getter and a transition metal oxide, the matrix phase (112) comprising mullite; forming an environmental barrier coating (108) on the bond coat (104), wherein the plurality of discrete particles (110), when fused, are contained within a matrix phase (112) between the surface (103) of the substrate (102) and an inner surface (103) of the environmental barrier coating (108); Including, The oxygen getter forms first discrete particles (111a) within the plurality of discrete particles (110), and the transition metal oxide forms second discrete particles (111b) within the plurality of discrete particles (110).

Images