Self-reinforcing environmental barrier coating

Abstract

A self-reinforced environmental barrier coating (EBC), a method for making the EBC, and an article containing the EBC are provided. The EBC is prepared from a composition of rare earth silicate and aluminum silicate at or near the eutectic point of the combination. The EBC forms a self-reinforced fibrous phase that reduces or eliminates microcracking.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Application No. 63 / 398,623, filed August 17, 2022, the disclosure of which is expressly incorporated herein by reference in its entirety.

[0002] FIELD OF THE INVENTION The present invention relates to compositions and methods for preparing self-reinforcing environmental barrier coatings, and to articles containing such coatings. [Background technology]

[0003] Components of high-temperature mechanical systems, such as gas turbine engines, are typically made from materials, such as ceramics and ceramic composites, that can withstand high temperatures. However, such materials can react with some elements and compounds present in the operating environment of the high-temperature mechanical system, such as water vapor. Reactions with environmental materials can result in damage to the component material and reduce the mechanical properties of the part, which can shorten the useful life of the component. Therefore, such components can be coated with an environmental barrier coating (EBC) that can reduce the exposure of the substrate to elements and compounds present in the operating environment of the high-temperature mechanical system.

[0004] Rare earth silicates are known for use in environmental barrier coatings, typically applied over bond coats. The air plasma spray (APS) process is often used for EBC deposition. However, rare earth silicate EBCs applied by APS are prone to the formation of microcracks within the as-sprayed APS coating. These microcracks can provide fast diffusion paths for oxidants, accelerating the oxidation of the bond coat (e.g., silicon bond coat), and potentially reducing the durability of the EBC.

[0005] To reduce crack formation, it has been reported that reinforcing fillers are added to the composition prepared for EBC, for example, SiC in the form of whiskers and / or nanoparticles (J. Ceramic. Soc. Japan, 129[4]209-216, (2021)).

[0006] There is a need for a rare earth silicate EBC applied by APS that is less susceptible to microcrack formation. Summary of the Invention

[0007] Compositions are provided that include rare earth silicate and aluminum silicate in proportions within 20 mole % or 15 mole % of the eutectic point of the composition.

[0008] Also provided is an article of manufacture comprising a substrate, a bond coat on the substrate, and an environmental barrier coat (EBC) on the bond coat, wherein the substrate preferably comprises a silicon-based ceramic matrix composite, the bond coat preferably comprises silicon, and the EBC preferably comprises a rare earth silicate and aluminum silicate composition, preferably within 20 mol % or 15 mol % of the eutectic point of the composition.

[0009] Also provided is a method of making an environmental barrier coating (EBC), comprising providing a substrate, applying a bond coat to the substrate, and applying a barrier coat to the bond coat, wherein applying the barrier coat preferably comprises applying a composition comprising a rare earth silicate and an aluminum silicate, preferably in proportions within 20 mol % or 15 mol % of the eutectic point of the composition.

[0010] Also provided is a method for producing a reinforcing fiber phase in a rare earth silicate coating (e.g., EBC), comprising obtaining a composition comprising a rare earth silicate and, preferably, aluminum silicate in a proportion within 20 mol % or 15 mol % of the eutectic point of the composition, and applying the composition to a substrate to form a rare earth silicate coating, wherein a fiber phase comprising the rare earth silicate is preferably formed in the rare earth silicate coating. The substrate preferably comprises a SiC ceramic, preferably a bond coat (preferably a silicon bond coat) on a surface of the SiC ceramic.

[0011] The composition is preferably in the form of a sintered powder. The composition is preferably obtained by agglomerating and sintering a mixture of rare earth silicate and aluminum silicate.

[0012] The rare earth silicate in the composition is preferably Yb2Si2O7. The aluminum silicate in the composition is preferably Al6Si2O 13 The rare earth silicate in the composition is preferably Yb2Si2O7, and the aluminum silicate in the composition is preferably Al6Si2O 13 is.

[0013] The proportion of rare earth silicate and aluminum silicate in the composition is preferably within 5 mole % of the eutectic point of the composition.

[0014] In one embodiment, the EBC is preferably Yb2Si2O7 and Al6Si2O 13 and more preferably contains 53 mol % to 83 mol % of Yb2Si2O7 and Al6Si2O 13 The composition preferably comprises 63 mol % to 73 mol % Yb2Si2O7 relative to the amount of the composition. Application of the composition to the substrate preferably comprises air plasma spraying.

[0015] The EBC preferably includes a reinforcing fiber phase.

[0016] Also provided is an article comprising an environmental barrier coating produced according to any of the above methods. The environmental barrier coating produced by this method preferably comprises a reinforcing fiber phase.

[0017] The reinforcing fiber phase preferably comprises a rare earth silicate. The reinforcing fiber phase preferably comprises Yb2Si2O7. [Brief explanation of the drawings]

[0018] [Figure 1] Schematic phase diagram of the rare earth silicate + Al6Si2O13 system. [Figure 2a] Figure 2a shows a typical microstructure of the agglomerated and sintered Yb2Si2O7-Al6Si2O13 composite powder at low magnification and Figure 2b shows a higher magnification. [Figure 2b] Figure 2a shows a typical microstructure of the agglomerated and sintered Yb2Si2O7-Al6Si2O13 composite powder at low magnification and Figure 2b shows a higher magnification. [Figure 3] Air plasma sprayed (APS) Yb2Si2O7 baseline coating showing muddy microcracks. [Figure 4] 1 is a Yb2Si2O7-9 mol % Al6Si2O13 baseline coating of APS showing microcracks and a few fibers. [Figure 5] Yb2Si2O7-17 mol % Al6Si2O13 coating of APS showing slight microcracking and a more fibrous morphology. [Figure 6] Yb2Si2O7-32 mol % Al6Si2O13 coating of APS showing fibrous morphology with no observed microcracks. [Figure 7] APS Yb2Si2O7-60 mol % Al6Si2O13 coating showing muddy microcracks. [Figure 8] APS Yb2Si2O7-84 mol % Al6Si2O13 coating showing muddy microcracks. [Figure 9]High magnification APS Yb2Si2O7-32 mol % Al6Si2O13 coating showing fiber details. EDX analysis (inset) shows the fiber is composed of the Yb2Si2O7 phase. [Figure 10a] The growth behavior of thermally grown oxide (TGO) on EBC is shown in Figure 10a (composition 1) and Figure 10b (composition 4), which are cross-sectional views of aged coatings. [Figure 10b] The growth behavior of thermally grown oxide (TGO) on EBC is shown in Figure 10a (composition 1) and Figure 10b (composition 4), which are cross-sectional views of aged coatings. DETAILED DESCRIPTION OF THE INVENTION

[0019] Environmental barrier coatings (EBCs) have been applied to silicon-based ceramic matrix composites (CMCs) to protect them from oxidation and water vapor attack. Currently, state-of-the-art EBC systems contain a silicon bond coat and an ytterbium silicate top coat. The air plasma spray (APS) process is commonly used for EBC deposition, but other methods are also used. Microcracks have always existed in APS ytterbium silicate top coatings. In high-temperature gas turbine engine environments, these microcracks provide fast diffusion paths for oxidants (water vapor and oxygen) to reach the silicon bond coat and accelerate silicon bond coat oxidation. EBCs spall when the thermally grown oxide (TGO) reaches a threshold thickness. Therefore, it is important to develop a tough EBC top coat that can suppress microcrack formation and thus enhance the high-temperature durability of EBCs in water vapor environments.

[0020] Unexpectedly, EBC topcoat compositions have been discovered that form self-reinforcing fibers and exhibit substantially reduced cracking. Material compositions and preparation methods for self-reinforced composite coatings are disclosed. The self-reinforced composite coating material is a composite of rare earth silicates (e.g., Yb2Si2O7) and aluminum silicates (e.g., mullite: Al6Si2O7). 13 )

[0021] It has been unexpectedly discovered that compositions of rare earth silicates and aluminum silicates at or near the eutectic temperature (see FIG. 1) form self-reinforced coatings with fibrous content that exhibit reduced or no microcracking when applied as an EBC. The EBC substantially reduces or prevents oxidation of the basecoat, resulting in a more durable EBC. As is known in the art, the eutectic point is an inherent property of the material combination.

[0022] EBCs prepared from the disclosed composite powders (i.e., aluminum silicate and rare earth silicate) exhibit higher erosion resistance than coatings prepared under the same conditions but from a baseline composition (i.e., aluminum silicate and no rare earth silicate). Erosion resistance can be measured by methods known in the art, including, for example, the ASTM G76 standard discussed below. Erosion resistance can be increased by at least 25%, at least 50%, at least 75%, or at least 100% compared to the baseline coating. While there is no preferred upper limit, erosion resistance is generally considered to be increased by no more than 150% compared to the baseline coating.

[0023] Without being bound by theory, it is believed that the reinforcing fiber phase contains rare earth elements primarily in the form of rare earth silicates. When the EBC composition approaches its eutectic point, the rare earth fiber phase is formed in situ during the formation of the environmental barrier coat.

[0024] Composite powder: EBC composites include any rare earth silicate and aluminum silicate that form a eutectic.

[0025] The rare earth silicate may be, for example, a monosilicate or disilicate of formula RE2Si2O7 or RE2SiO5, where RE is a rare earth element such as Y, Yb, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Lu, preferably Yb.

[0026] The content of rare earth silicate can be expressed as the mole percent of rare earth silicate relative to the total of rare earth silicate and aluminum silicate. Referring to Figure 1, the preferred rare earth silicate content is at the eutectic point. The amount of rare earth silicate may be 1 mole %, 5 mole %, 10 mole %, 15 mole %, or 20 mole % lower than the eutectic. The amount of rare earth silicate may be 1 mole %, 5 mole %, 10 mole %, 15 mole %, or 20 mole % higher than the eutectic. Ranges formed by the combination of the lower and upper limits are contemplated and are preferred. For example, some preferred ranges include 1 mol% below the eutectic point to 1 mol% above the eutectic point, 1 mol% below the eutectic point to 5 mol% above the eutectic point, 5 mol% below the eutectic point to 1 mol% above the eutectic point, 5 mol% below the eutectic point to 5 mol% above the eutectic point, 5 mol% below the eutectic point to 10 mol% above the eutectic point, 10 mol% below the eutectic point to 5 mol% above the eutectic point, and 10 mol% below the eutectic point to 10 mol% above the eutectic point. mol% higher than the eutectic point, 10 mol% lower than the eutectic point to 15 mol% higher than the eutectic point, 15 mol% lower than the eutectic point to 10 mol% higher than the eutectic point, 15 mol% lower than the eutectic point to 15 mol% higher than the eutectic point, 20 mol% lower than the eutectic point to 15 mol% higher than the eutectic point, 15 mol% lower than the eutectic point to 20 mol% higher than the eutectic point, and 20 mol% lower than the eutectic point to 20 mol% higher than the eutectic point.

[0027] For example, if rare earth silicate and mullite have a eutectic point at 70 mol% rare earth silicate, some preferred ranges of these components would include (among others) 50-90 mol% rare earth silicate, 50-85 mol% rare earth silicate, 55-80 mol% rare earth silicate, 65-75 mol% rare earth silicate, and 60-75 mol% rare earth silicate. Where a stated range includes 1 mol% or 99 mol% rare earth silicate, it should be understood that the corresponding endpoints of that range are 1 mol% or 99 mol%, respectively.

[0028] Ranges may also be expressed in terms of the eutectic point as follows: EP is defined as the mole percent of rare earth silicate (e.g., ytterbium disilicate) at the eutectic point relative to the sum of the rare earth silicate and aluminum silicate (e.g., mullite). EP is an inherent property of a particular rare earth silicate + aluminum silicate combination. Some preferred ranges include (EP - 20 mol%) to (EP + 20 mol%), (EP - 15 mol%) to (EP + 15 mol%), (EP - 10 mol%) to (EP + 10 mol%), (EP - 5 mol%) to (EP + 5 mol%), (EP - 1 mol%) to (EP + 1 mol%), (EP - 5 mol%) to (EP + 1 mol%), and (EP - 1 mol%) to (EP + 5 mol%). These may be expressed as within 20 mole percent of the eutectic point, within 15 mole percent of the eutectic point, within 10 mole percent of the eutectic point, within 5 mole percent of the eutectic point, and within 1 mole percent of the eutectic point.

[0029] A proportion of ytterbium disilicate should be used for in situ growth of Yb2Si2O7 fibers in the coating. Ytterbium disilicate and mullite are believed to have a eutectic point at about 68 mole percent ytterbium disilicate. Some preferred ranges for these components include 48-58 mole percent ytterbium disilicate, 53-83 mole percent ytterbium disilicate, 58-78 mole percent ytterbium disilicate, and 58-73 mole percent ytterbium disilicate. Yb2Si2O7-Al6Si2O 13Other preferred ranges for Yb2Si2O7 in the composite include 57 mol% to 83 mol%, 63 to 73 mol%, and 67 to 69 mol%.

[0030] The composite powder preferably consists of rare earth silicates and aluminum silicates apart from impurities such as Na2O, TiO2, CaO, MgO, etc. The impurities may constitute less than 0.5% by weight.

[0031] The composite powder may also include a reinforcing filler (i.e., for example, SiC nanoparticles and / or whiskers). If present, the composite powder preferably includes no more than 20 wt.%, no more than 15 wt.%, no more than 10 wt.%, no more than 5 wt.% of the reinforcing filler, based on the total weight of the rare earth silicate, aluminum silicate, and reinforcing filler. Preferably, the composite powder is free of reinforcing filler (0 wt.%).

[0032] Composite powder manufacturing: Composite powders according to the present disclosure can be made by any suitable method by one skilled in the art. Some suitable methods include: -Blending -agglomeration agglomeration and sintering, and -Melting and crushing.

[0033] Agglomeration and sintering is the preferred method. Figures 2a and 2b show the agglomerated and sintered Yb2Si2O7-Al6Si2O 13 1 shows a typical microstructure of a composite powder.

[0034] Any particle size distribution of a composition suitable for powder manufacturing methods and coating formation methods can be determined by one skilled in the art. For example, Yb2Si2O7(YbDS)-Al6Si2O 13Typical particle size distributions for composite powders can be 5 μm, 10 μm, 11 μm, 20 μm, 30 μm, or 40 μm or greater, and 150 μm, 105 μm, 100 μm, 90 μm, 70 μm, 62 μm, or 60 μm or less. Ranges formed by pairs of these smaller and larger sizes are included. Some preferred ranges include, for example, 40 μm to 60 μm, 11 μm to 105 μm, 11 μm to 62 μm, 5 μm to 150 μm, 10 μm to 150 μm, 10 μm to 100 μm, 20 μm to 90 μm, and 30 μm to 70 μm.

[0035] Coating production: Any method of applying the EBC can be used, as determined by one of skill in the art. Some suitable methods include: -Atmospheric Plasma Spraying (APS), -High velocity oxy-fuel spray (HVOF), -Combustion spraying, -Vacuum plasma spray (VPS), and -Suspension spraying.

[0036] The EBC is preferably applied by APS. The parameters of the APS coating can be determined by one skilled in the art. Some typical process parameters include: Current: 200~800A, Voltage: 50~150V, Power: 10~120kW, Ar flow rate: 50~100nlpm H2 flow rate: 1~10nlpm Powder feeding rate: 1~100g / min Spraying distance: 50~250mm

[0037] Any method of applying a bond coat (e.g., silicon) to a substrate can be used, including thermal spray processes such as APS, VPS, HVOF, combustion spray, and suspension spray, as determined by one skilled in the art. APS is preferred.

[0038] Yb3Al5O 12 It is believed that small amounts of rare earth aluminate reaction products, such as aluminum silicate, rare earth aluminate, and rare earth silicate may be formed in situ during the formation of the EBC. If present, the amount formed in the EBC is believed to be less than 3 mole % based on the combined total of rare earth silicate, aluminum silicate, and rare earth aluminate reaction products. [Example]

[0039] Example 1: As shown in Table 1, Yb2Si2O7 and Al6Si2O 13 Six batches were prepared, which were agglomerated and sintered, with various ratios of Yb2Si2O7 and Al6Si2O 13 The powders were mixed in an aqueous slurry and spray dried to form agglomerated spherical powders, which were then sintered at 1300°C, and the sintered powder was then sieved to -62 +11 μm.

[0040] [Table 1]

[0041] The coatings were applied to the SiC ceramic surface as follows: For each of Compositions 1-6, a Si bond coat was applied to the SiC ceramic surface using APS. The corresponding composition was then applied onto the Si bond coat using APS. The APS process parameters are listed in Table 2.

[0042] [Table 2]

[0043] SEM images of the APS coating surfaces prepared from compositions 1 to 6 are shown in Figures 3 to 8, respectively.

[0044] The comparative example of the baseline Yb2Si2O7 coating, Composition 1 (Figure 3), which does not contain aluminum silicate, showed a significant number of microcracks.

[0045] Yb2Si2O7-Al6Si2O 13 In composite coatings, Al6Si2O 13 As the mole percentage of increased (Figures 4 and 5), the number of microcracks decreased, but a more fibrous morphology appeared.

[0046] Yb2Si2O7-32 mol% Al6Si2O 13 No microcracks were observed in the composite coating (Fig. 6).

[0047] Al6Si2O 13 As the mole percentage of was further increased, the fibrous morphology decreased and the coating began to show more microcracks (Figures 7 and 8).

[0048] The result is Yb2Si2O7-Al6Si2O 13 Optimal Al6Si2O in composites 13 is about 32 mol % for the microcrack-free coating with fibrous morphology (Fig. 6).

[0049] Yb2Si2O7-32 mol% Al6Si2O 13 A high magnification photomicrograph of the composite coating is shown in Figure 9. Elemental analysis of the fibrous portion of the EBC shows that it contains ytterbium primarily in the Yb2Si2O7 phase.

[0050] The protective capabilities of Compositions 1 and 4 were compared as follows. A silicon bond coating was applied to two SiC ceramic surfaces as described above. One surface was then APS coated as described above with EBC from Comparative Composition 1, and the other surface was coated with EBC from Composition 4. The coated surfaces were then exposed to a 90% by volume HO-10% by volume air environment at 1,316°C for 510 hours. Cross-sectional photomicrographs are shown in Figure 10a (Composition 1) and Figure 10b (Composition 4).

[0051] Figure 10a shows the growth of thermally grown oxide (TGO) with a thickness of about 13.5 μm. Figure 10b shows the growth of TGO with a thickness of about 0.7 μm, which is about 1 / 20 of the amount of the control sample. Self-reinforced Yb2SiO7-32 mol% Al6SiO on a Si bond coat 13 TGO growth in appears to be about 20 times slower than that in the baseline Yb2Si2O7 on Si bond coat.

[0052] Example 2: EBCs prepared from Composition 1 (baseline) and Composition 4 were prepared as in Example 1 and tested for hardness and erosion resistance.

[0053] Rockwell hardness was measured using the HR15N method.

[0054] The erosion resistance of the coating was measured using an erosion test rig according to ASTM G76 standard. Specifically, aluminum oxide powder with particle sizes ranging from 40 to 80 mm was used as the erodent. The erodent was accelerated onto the EBC surface at a 20° angle at room temperature until a specific dose of approximately 600 g was delivered. The depth of the eroded crater was then measured. The erosion resistance was expressed in seconds per mil and represents the time required to erode 1 mil of coating thickness. A higher erosion resistance number indicates better erosion resistance.

[0055] The results are shown in Table 3.

[0056] [Table 3]

[0057] The fibrous coating prepared from Composition 4, which has a self-reinforced microstructure, exhibited approximately twice the erosion resistance compared to the non-self-reinforced baseline EBC coating prepared from Composition 1. Additionally, due to the crack-free microstructure, the self-reinforced coating hardness was also slightly improved compared to the baseline.

Claims

1. A composition comprising a rare earth silicate and an aluminum silicate in proportions within 20 mole percent of the eutectic point of said composition.

2. The composition of claim 1 in the form of a sintered powder.

3. The rare earth silicate is Yb ２ Si ２ O ７ 2. The composition of claim 1, wherein:

4. The aluminum silicate is Al ６ Si ２ O １３ 2. The composition of claim 1, wherein:

5. The aluminum silicate is Al ６ Si ２ O １３ The composition of claim 4, wherein

6. 2. The composition of claim 1, wherein said percentage is within 5 mole percent of said eutectic point of said composition.

7. The rare earth silicate is Yb ２ Si ２ O ７ and the aluminum silicate is Al ６ Si ２ O １３ The composition of claim 6, wherein

8. 1. An article of manufacture comprising: a substrate; a bond coat on the substrate; and an environmental barrier coat (EBC) on the bond coat, the substrate comprises a silicon-based ceramic matrix composite; the bond coat comprises silicon; An article wherein the EBC comprises a rare earth silicate and aluminum silicate composition in a proportion within 20 mole percent of the eutectic point of the composition.

9. The rare earth silicate is Yb ２ Si ２ O ７ and the aluminum silicate is Al ６ Si ２ O １３ 9. The article of claim 8, wherein:

10. 10. The article of claim 9, wherein said percentage is within 5 mole percent of said eutectic point of said composition.

11. The EBC is Yb ２ Si ２ O ７ and Al ６ Si ２ O １３ 53 mol % to 83 mol % of Yb ２ Si ２ O ７ 10. The article of claim 9, comprising:

12. The EBC is ２ Si ２ O ７ and Al ６ Si ２ O １３ 63 mol % to 73 mol % of Yb ２ Si ２ O ７ The article of claim 10 comprising:

13. The article of claim 8 , wherein the EBC comprises a reinforcing fiber phase.

14. The article of claim 10 , wherein the EBC comprises a reinforcing fiber phase.

15. 1. A method of making an environmental barrier coating, comprising: Providing a substrate; applying a bond coat to the substrate; applying a barrier coat to the bond coat; The method wherein applying the barrier coat comprises applying a composition comprising a rare earth silicate and an aluminum silicate in proportions within 20 mole percent of the eutectic point of the composition.

16. The method of claim 15 , wherein applying the composition comprises air plasma spraying.

17. 16. The method of claim 15, wherein the composition is obtained by agglomerating and sintering a mixture of the rare earth silicate and aluminum silicate.

18. The rare earth silicate is Yb ２ Si ２ O ７ and the aluminum silicate is Al ６ Si ２ O １３ and the composition is Yb ２ Si ２ O ７ and Al ６ Si ２ O １３ 63 mol % to 73 mol % of Yb ２ Si ２ O ７ 16. The method of claim 15, comprising:

19. 16. An article comprising an environmental barrier coating made according to claim 15.

20. 20. The article of claim 19, wherein the barrier coat comprises a reinforcing fiber phase.

21. 20. An article comprising an environmental barrier coating made according to claim 18.

22. 22. The article of claim 21, wherein the barrier coat comprises a reinforcing fiber phase.

23. 1. A method for producing a reinforcing fiber phase in a rare earth silicate coating, comprising: obtaining a composition comprising rare earth silicate and aluminum silicate in proportions within 20 mole percent of the eutectic point of the composition; applying the composition to a substrate to form a rare earth silicate coating; The method wherein a fibrous phase comprising the rare earth silicate is formed in the rare earth silicate coating.

24. 24. The method of claim 23, wherein applying the composition comprises air plasma spraying.

25. 24. The method of claim 23, wherein the composition is obtained by agglomerating and sintering a mixture of the rare earth silicate and aluminum silicate.

26. The rare earth silicate is Yb ２ Si ２ O ７ and the aluminum silicate is Al ６ Si ２ O １３ and the composition is Yb ２ Si ２ O ７ and Al ６ Si ２ O １３ 63 mol % to 73 mol % of Yb ２ Si ２ O ７ 24. The method of claim 23, comprising:

27. 24. An article comprising a rare earth silicate coating made according to claim 23.

28. 28. The article of claim 27, wherein the reinforcing fiber phase comprises the rare earth silicate.

29. 27. An article comprising a rare earth silicate coating made according to claim 26.

30. The reinforcing fiber phase is Yb ２ Si ２ O ７ 30. The article of claim 29, comprising:

31. 24. The method of claim 23, wherein the substrate comprises a silicon coating on a SiC ceramic surface.

32. 2. The composition of claim 1, wherein said percentage is within 15 mole percent of said eutectic point of said composition.

33. 9. The article of manufacture of claim 8, wherein said percentage is within 15 mole percent of said eutectic point of said composition.

34. 16. The method of making an environmental barrier coating of claim 15, wherein said percentage is within 15 mole percent of said eutectic point of said composition.

35. 24. The method of producing a reinforcing fiber phase according to claim 23, wherein said proportion is within 15 mole percent of said eutectic point of said composition.

36. 10. The article of manufacture of claim 8, wherein the EBC has an erosion resistance that is at least 25% greater than a second EBC similarly prepared but lacking any rare earth silicate.

37. 16. The method of making an environmental barrier coating of claim 15, wherein the barrier coat has an erosion resistance that is at least 25% greater than a second barrier coat similarly prepared but lacking any rare earth silicate.

38. 24. The method of producing a reinforcing fiber phase in a rare earth silicate coating of claim 23, wherein the rare earth silicate coating has an erosion resistance that is at least 25% greater than a similarly prepared second coating that does not contain any rare earth silicate.

39. The rare earth silicate is Yb ２ Si ２ O ７ and the aluminum silicate is Al ６ Si ２ O １３ and the Yb ２ Si ２ O ７ and the Al ６ Si ２ O １３ 48 mol % to 88 mol % of the Yb ２ Si ２ O ７ The composition of claim 1 comprising:

40. The Yb ２ Si ２ O ７ and the Al ６ Si ２ O １３ 53 mol % to 83 mol % of the Yb ２ Si ２ O ７ 40. The composition of claim 39, comprising:

41. The Yb ２ Si ２ O ７ and the Al ６ Si ２ O １３ 63 mol % to 73 mol % of the Yb ２ Si ２ O ７ 41. The composition of claim 40, comprising:

Images