Alumina-rich aluminosilicate diffusion barriers for multilayer environmental barrier coatings

Abstract

A method for forming an environmental barrier coating (EBC) system on a surface of a ceramic matrix composite (CMC) to be protected, and the EBC, the method comprising applying an aluminosilicate composition onto the surface of the CMC to be protected to form an aluminosilicate layer, and applying a rare earth disilicate composition onto the aluminosilicate layer.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This international application claims the benefit / priority of U.S. Provisional Patent Application No. 63 / 405,025, filed September 9, 2022, the disclosure of which is expressly incorporated herein by reference in its entirety. [Background technology]

[0002] FIELD OF THE INVENTION Embodiments relate to methods of forming environmental barrier coatings (EBCs) required to protect SiC-based ceramic matrix composite (CMC) components from water vapor attack, and the structure of the EBCs so formed.

[0003] (Background Information Discussion) Environmental barrier coatings (EBCs) have been applied to Si-based CMCs to protect them from oxidation and water vapor attack. Current EBC systems consist of a silicon bond coat layer applied to the SiC CMC substrate surface to be protected, followed by one or more protective rare-earth disilicate (e.g., Yb2SiO7) coating layers as topcoats. During the operational life of a CMC component, oxidizers such as water vapor and oxygen can diffuse through the EBC layer and oxidize the Si-based bond coat, resulting in the growth of a cristobalite SiO2 thermally grown oxide (TGO) layer. This cristobalite SiO2 TGO growth is the primary cause of EBC failure. Such EBCs will spall once the TGO reaches a threshold thickness. Therefore, it is important to slow the TGO growth rate and improve the durability of EBC coatings. Summary of the Invention

[0004]

[0003] Embodiments relate to a method for forming an environmental barrier coating system (EBC) that includes applying a low-oxidation diffusion barrier layer between a rare earth disilicate layer and a Si-based bond coat to reduce undesirable TGO growth rates. The low-oxidation diffusion barrier layer specifically comprises an Al2O3-rich aluminosilicate composition, which may be, for example, 75-100% Al2O3 weight percent, preferably 77%-87% Al2O3, with the remainder being SiO2. The reason for selecting an Al2O3-rich aluminosilicate is two-fold: 1) Al2O3-rich aluminosilicate has a low oxidation diffusion coefficient and can slow down the oxidant diffusion. 2) Excess Al2O3, i.e., more than 75% Al2O3 in Al2O3-rich aluminosilicate, can react with cristobalite SiO2 TGO to form two phases, Al2O3 + mullite phase, thus changing the TGO chemistry and avoiding cristobalite SiO2 phase transformation during thermal cycling.

[0005] To reduce the TGO growth rate in EBCs, a low oxidant / oxidation diffusion barrier layer is formed between a rare earth disilicate layer on the surface of a substrate, preferably a CMC component, and a Si-based bond coat layer. The oxidation diffusion barrier layer includes an Al2O3-rich aluminosilicate composition that has a low oxidant / oxidation diffusion coefficient and can slow down oxidant diffusion. Furthermore, because excess Al2O3 can react with cristobalite SiO2 TGO to form a mullite phase, the chemistry of the TGO can be altered to avoid cristobalite SiO2 phase transformation during thermal cycling.

[0006] Water vapor tests of EBCs according to embodiments conducted at 1400°C for 170 and 410 hours showed that TGO growth in multilayer EBCs, i.e., EBCs with an Al2O3-rich aluminosilicate interlayer, was approximately three times slower than in conventional EBCs, i.e., EBCs without an Al2O3-rich aluminosilicate interlayer.

[0007] The Al2O3-rich aluminosilicate coating can be deposited by air plasma spraying, low-pressure plasma spraying, high-velocity oxygen flame spraying, suspension thermal spraying, slurry coating processes, chemical vapor deposition, or physical vapor deposition. Furthermore, for thermal spraying, the Al2O3-rich aluminosilicate feed powder can be melt-crushed, spray-dried, agglomerated and sintered, or plasma-densified. The particle size in the Al2O3-rich aluminosilicate feed powder can range from 11 μm to 105 μm, preferably from 11 μm to 62 μm.

[0008] The Al2O3-rich aluminosilicate coating layer formed on the multilayer EBC according to the embodiment has a porosity in the range of greater than 0% to 5% and a thickness in the range of 0.5 μm to 100 μm, preferably in the range of 1 to 50 μm, and more preferably in the range of 5 to 20 μm.

[0009] Embodiments relate to a method for forming an environmental barrier coating (EBC) system on a surface of a ceramic matrix composite (CMC) to be protected, the method including applying an aluminosilicate composition onto the surface of the CMC to be protected to form an aluminosilicate layer, and applying a rare earth disilicate composition onto the aluminosilicate layer.

[0010] In an embodiment, the CMC may include a SiC / SiC CMC.

[0011] According to another embodiment, the method may further include applying a Si-based bond coat layer directly onto the surface of the CMC to be protected. The aluminosilicate layer is applied directly onto the Si-based bond coat layer.

[0012] According to embodiments, the aluminosilicate composition may include an Al2O3-rich aluminosilicate composition comprising at least 75 wt% Al2O3, and the aluminosilicate layer may include an Al2O3-rich aluminosilicate layer. The Al2O3-rich aluminosilicate composition may include more than 75 wt% Al2O3. Furthermore, the Al2O3-rich aluminosilicate composition may include pure Al2O3. The Al2O3-rich aluminosilicate layer may be formed by one of thermal spray deposition, a slurry coating process, chemical vapor deposition, or physical vapor deposition. Still further, when the Al2O3-rich aluminosilicate layer is formed by thermal spray deposition, the Al2O3-rich aluminosilicate feedstock may include fused / milled particles, spray-dried particles, agglomerated and sintered particles, or plasma-densified particles. The particle size range of the Al2O3-rich aluminosilicate feedstock may be 11 μm to 105 μm, preferably 11 μm to 62 μm. The Al2O3-rich aluminosilicate layer may have a porosity greater than 0% and less than 5%, and a thickness in the range of 0.5 μm to 100 μm, preferably 1 μm to 50 μm, more preferably 5 μm to 20 μm.

[0013] According to other embodiments, the rare earth disilicate composition comprises Yb2Si2O7, Er2Si2O7, Lu2Si2O7, or (YbYLuEr)2Si2O7.

[0014] Embodiments relate to an environmental barrier coating (EBC) system formed on the surface of a ceramic matrix composite (CMC) to be protected according to the methods described above.

[0015] According to an embodiment, the CMC may include a SiC / SiC CMC.

[0016] According to another embodiment, the EBC may further include a Si-based bond coat layer directly on the surface of the CMC to be protected. An aluminosilicate layer may be present directly on the Si-based bond coat layer.

[0017] In yet other embodiments, the aluminosilicate layer may have an Al2O3-rich aluminosilicate composition comprising at least 75 wt% Al2O3, and the rare earth disilicate layer may include a Yb2Si2O7, Er2Si2O7, Lu2Si2O7, or (YbYLuEr)2Si2O7 composition.

[0018] Embodiments relate to an environmental barrier coating (EBC) system that includes an aluminosilicate layer and a rare earth disilicate layer formed on the aluminosilicate layer.

[0019] According to an embodiment, the EBC may also include a Si-based bond coat layer, and the aluminosilicate layer may be applied directly onto the Si-based bond coat layer.

[0020] In other embodiments, the aluminosilicate layer can have an Al2O3-rich aluminosilicate composition comprising at least 75 wt% Al2O3. The Al2O3-rich aluminosilicate composition can comprise greater than 75 wt% Al2O3. Additionally, the Al2O3-rich aluminosilicate composition can comprise pure Al2O3. The Al2O3-rich aluminosilicate layer has a porosity greater than 0% and less than 5%, and a thickness ranging from 0.5 μm to 100 μm, preferably from 1 μm to 50 μm, and more preferably from 5 μm to 20 μm.

[0021] According to still yet other embodiments, the rare earth disilicate layer may include Yb2Si2O7, Er2Si2O7, Lu2Si2O7, or (YbYLuEr)2Si2O7 compositions.

[0022] Other exemplary embodiments and advantages of the present invention can be ascertained by reviewing this disclosure and the accompanying drawings. [Brief explanation of the drawings]

[0023] The present invention is further described in the following detailed description with reference to the several drawings, in which like reference numerals represent like parts throughout the several views, and in which: [Figure 1A] 1 illustrates a schematic representation of a multi-layer EBC according to an embodiment. [Figure 1B] 1 illustrates a schematic representation of a multi-layer EBC according to an embodiment. [Figure 2] The Al2O3-SiO2 phase diagram is shown below. [Figure 3] 1 shows the diffusion coefficient of oxygen as a function of temperature. [Figure 4A] 1 shows an SEM image of the microstructure of a known EBC. [Figure 4B] 1 shows an SEM image of the microstructure of an EBC according to an embodiment. [Figure 4C] 1 shows an SEM image of the microstructure of an EBC according to an embodiment. [Figure 5A] The TGO growth behavior in known EBCs is shown. [Figure 5B] 1 shows TGO growth behavior in an EBC according to an embodiment evaluated at 1400° C. in 90 vol. % HO-10 vol. % air for 170 hours; and [Figure 5C] 1 shows TGO growth behavior in an EBC according to an embodiment evaluated at 1400° C. in 90 vol. % HO-10 vol. % air for 170 hours; and [Figure 6A] The growth behavior of TGO in known EBCs is shown. [Figure 6B] 10 shows TGO growth behavior in an EBC according to an embodiment evaluated at 1400° C. in 90 vol. % H2O-10 vol. % air for 410 hours. [Figure 6C] 10 shows TGO growth behavior in an EBC according to an embodiment evaluated at 1400° C. in 90 vol. % H2O-10 vol. % air for 410 hours. DETAILED DESCRIPTION OF THE INVENTION

[0024] The details shown in this specification are examples and are for the purpose of exemplary description of embodiments of the present invention only, and are presented to provide what is believed to be the most useful and easily understood explanation of the principles and conceptual aspects of the present invention. In this regard, no attempt has been made to show the structural details of the present invention in more detail than is necessary for a fundamental understanding of the present invention, and the description taken together with the drawings will make clear to those skilled in the art how several forms of the present invention may be embodied in practice.

[0025] A coating system, particularly an EBC coating system having an Al2O3-rich aluminosilicate composition layer, is deposited on the surface of a SiC / SiC ceramic matrix composite (CMC) component or on a Si-based bond coat layer in a multilayer EBC system. The Al2O3-rich aluminosilicate coating layer can slow down oxidant diffusion and significantly reduce the TGO growth rate, while excess Al2O3 in the Al2O3-rich aluminosilicate coating layer can consume and react with the growing SiO2 TGO, thus changing the TGO growth behavior. The Al2O3 concentration in the Al2O3-rich aluminosilicate composition is, for example, greater than 75 weight percent, with the remainder being SiO2.

[0026] TGO growth is highly dependent on the composition, microstructure, and architecture of the coating material. To reduce the TGO growth rate, a low oxidant / oxidation diffusion barrier layer is applied between the rare earth disilicate layer and the Si-based bond coat, which can slow down oxidant diffusion. In embodiments, the oxidation diffusion barrier layer can include an Al2O3-rich aluminosilicate composition. The Al2O3-rich aluminosilicate layer of the oxidation diffusion barrier layer is advantageous because it has a low oxidant diffusion coefficient, which can slow down oxidant diffusion. Furthermore, excess Al2O3 in the Al2O3-rich aluminosilicate layer can react with the cristobalite SiO2 TGO to form a mullite phase, which can change the chemistry of the TGO and prevent cristobalite SiO2 phase transformation during thermal cycling.

[0027] 1A and 1B show exemplary embodiments of EBC coating systems 1, 1′ formed on a SiC CMC component 2. The three-layer EBC coating system in FIG. 1A includes a rare earth disilicate layer 3, e.g., YbSiO, ErSiO, LuSiO, (YbYLuEr)SiO, etc., disposed on an AlO-rich aluminosilicate layer 4, and a Si-based bond coat 5 applied to the SiC CMC 2. In FIG. 1B, the two-layer EBC coating system 1′ includes a rare earth disilicate layer 3, e.g., YbSiO, ErSiO, LuSiO (YbYLuEr)SiO, etc., formed on an AlO-rich aluminosilicate layer 4 applied to a SiC CMC (or SiC / SiC CMC) 2 with a Si-based bond coat layer. In some applications, the two-layer EBC coating system 1' may be used without a Si-based bond coating layer, so that an alumina-rich aluminosilicate can be applied directly to the SiC / SiC CMC to protect the CMC. Furthermore, the alumina-rich aluminosilicate will slow down the TGO growth rate, as the SiC surface will oxidize to form a SiO TGO layer. Furthermore, because the melting point of silicon is approximately 1414°C, the two-layer EBC coating system 1' may be advantageous in high-temperature environments above 1400°C.

[0028] The Al2O3-rich aluminosilicate coating layer of the EBC coating system 1, 1' can be formed via thermal spray deposition, including air plasma spray deposition, low-pressure plasma spray deposition, high-velocity oxygen flame spray deposition, and suspension spray deposition; slurry coating processes; chemical vapor deposition; or physical vapor deposition. Furthermore, when the intermediate coating is applied by one of the thermal spray deposition processes, the Al2O3-rich aluminosilicate feedstock powder can be produced via melting / milling particles, spray-drying particles, agglomerating and sintering particles, or plasma densifying particles. The particle size in the Al2O3-rich aluminosilicate feedstock ranges from 11 μm to 105 μm, preferably from 11 μm to 62 μm.

[0029] The Al2O3-rich aluminosilicate intermediate coating in the EBC system 1, 1' may have a porosity greater than 0% and less than 5%, and a thickness in the range of 0.5 μm to 100 μm, preferably 1 μm to 50 μm, more preferably 5 μm to 20 μm.

[0030] Figure 2 shows the Al2O3-SiO2 phase diagram from Frederic J. Klug et al., "Alumina-Silica Phase Diagram in the Mullite Region," J. Am. Ceram. Soc., Vol. 70, No. 10, pp. 750-59 (1987). In Figure 2, it can be seen that the Al2O3-rich aluminosilicate material forming the Al2O3-rich aluminosilicate layer 3 of Figures 1A and 1B, e.g., at greater than 75 wt. % Al2O3, contains excess alumina compared to stoichiometric mullite. This excess Al2O3 has been found to react with and consume the SiO2 TGO, thus altering the TGO growth behavior. Furthermore, Figure 3 from Franck Nozahic et al., "Self-healing thermal barrier coating systems fabricated by spark plasma sintering," Materials & Design, 2018, No. 143, pp. 204-213 (2018) shows the diffusion coefficient of oxygen as a function of temperature for various compositions including alumina and mullite. As shown in Figure 3, Al2O3 and mullite have low diffusion coefficients of oxygen compared to other compositions.

[0031] Figure 4A shows SEM images of the microstructure of a known two-layer EBC system consisting of a rare earth disilicate layer, such as YbSiO, ErSiO, LuSiO, or (YbYLuEr)SiO, and a Si-based bond coat layer. Figure 5A shows the growth behavior of TGO (approximately 6.9 μm) on the Si bond coat layer when the known two-layer EBC system of Figure 4A was evaluated at 1400 °C for 170 hours in a 90% HO-10% air environment. Figure 6A shows the continuous growth behavior of TGO (approximately 9.2 μm) on the Si bond coat layer when the known two-layer EBC system of Figure 4A was evaluated at 1400 °C for 410 hours in a 90% HO-10% air environment.

[0032] In an exemplary embodiment, although an extreme example, Figure 4B shows an SEM image of the microstructure of a three-layer EBC system including a rare earth disilicate layer such as YbSiO, ErSiO, LuSiO, or (YbYLuEr)SiO, an AlO-rich aluminosilicate composition layer, i.e., a pure AlO intermediate layer (no SiO), and a Si-based bond coat layer. Figure 5B shows the growth behavior of TGO (approximately 1.7 μm) on the Si bond coat layer when the EBC system of Figure 4B was evaluated in a 90% HO-10% air environment at 1400 °C for 170 hours. Furthermore, because this pure Al2O3 composition has an Al2O3 concentration in the Al2O3-rich aluminosilicate composition greater than 75 weight percent (the remainder is SiO2), this excess Al2O3 can consume and react with the grown SiO2 TGO, thus altering the TGO growth behavior. As shown in Figure 5B, it can be seen that the excess Al2O3 in the interlayer, i.e., greater than 75 weight percent Al2O3, is converted to mullite phase due to this reaction between Al2O3 and SiO2. Figure 6B shows the continuous growth behavior of TGO (approximately 2.7 μm) on the Si bond coating layer when the EBC system of Figure 4B was evaluated in a 90% HO-10% air environment at 1400 °C for 410 hours. Additional mullite phase resulting from the continuous reaction between Al2O3 and SiO2 can be observed in the Al2O3 interlayer in Figure 6B, and the SiO2 TGO diffuses into the Al2O3 interlayer and reacts with Al2O3.

[0033] In another exemplary embodiment, Figure 4C shows an SEM image of the microstructure of a three-layer EBC system including a rare earth disilicate layer, such as YbSiO, ErSiO, LuSiO, or (YbYLuEr)SiO, an AlO-rich aluminosilicate composition layer, i.e., alumina-mullite consisting of 77 wt% AlO-23 wt% SiO, and a Si-based bond coat layer. Figure 5C shows the growth behavior of TGO (approximately 1.8 μm) on the Si bond coat layer when the EBC system of Figure 4C was evaluated in a 90% HO-10% air environment at 1400 °C for 170 hours. FIG. 6C shows the continuous growth behavior of TGO (approximately 3.5 μm) on the Si bond coating layer when the EBC system of FIG. 4C was evaluated in a 90% HO-10% air environment at 1400°C for 410 hours.

[0034] Thus, it is apparent that the exemplary embodiments described above in FIGS. 4B (and 5B and 6B) and 4C (and 5C and 6C) having an Al2O3-rich aluminosilicate intermediate layer are very effective in slowing down the TGO growth rate in EBCs compared to EBCs without an Al2O3-rich aluminosilicate layer, such as in FIG. 4A (and 5A and 6A).

[0035] It should be noted that the foregoing examples are provided for illustrative purposes only and are not to be construed as limiting the invention in any way. While the invention has been described with reference to exemplary embodiments, it should be understood that the terms used herein are terms of description and illustration, rather than of limitation. Changes may be made within the purview of the appended claims, as presently stated and amended, without departing from the scope and spirit of the invention in its aspects. While the invention has been described herein with reference to particular means, materials, and embodiments, the invention is not intended to be limited to the details disclosed herein. Rather, the invention extends to all functionally equivalent structures, methods, and uses, as fall within the scope of the appended claims.

Claims

1. 1. A method for forming an environmental barrier coating (EBC) system on a surface of a ceramic matrix composite (CMC) to be protected, comprising: applying an aluminosilicate composition onto the surface of the CMC to be protected to form an aluminosilicate layer; applying a rare earth disilicate composition onto the aluminosilicate layer.

2. The method of claim 1 , wherein the CMC comprises a SiC / SiC CMC.

3. further comprising applying a Si-based bond coat layer directly onto the surface of the CMC to be protected; The method of claim 1 or 2, wherein the aluminosilicate layer is applied directly onto the Si-based bond coat layer.

4. The aluminosilicate composition is at least 75 wt. % Al ２ O ３ Al containing ２ O ３ rich aluminosilicate composition, The aluminosilicate layer is Al ２ O ３ The method of any one of claims 1 to 3, comprising a rich aluminosilicate layer.

5. The Al ２ O ３ The rich aluminosilicate composition contains more than 75 wt.% Al ２ O ３ The method of claim 4, comprising:

6. The Al ２ O ３ The rich aluminosilicate composition is preferably pure Al ２ O ３ The method of claim 4, comprising:

7. The Al ２ O ３ 5. The method of claim 4, wherein the rich aluminosilicate layer is formed by one of thermal spray deposition, a slurry coating process, chemical vapor deposition, or physical vapor deposition.

8. The Al ２ O ３ When the Al-rich aluminosilicate layer is formed by thermal spray deposition, ２ O ３ 8. The method of claim 7, wherein the rich aluminosilicate feedstock comprises fused / milled particles, spray-dried particles, agglomerated and sintered particles, or plasma-densified particles.

9. The Al ２ O ３ 9. The process of claim 8, wherein the particle size range of the rich aluminosilicate feedstock is from 11 μm to 105 μm, preferably from 11 μm to 62 μm.

10. The Al ２ O ３ 5. The method of claim 4, wherein the rich aluminosilicate layer has a porosity greater than 0% and less than 5% and a thickness in the range of 0.5 μm to 100 μm, preferably 1 μm to 50 μm, more preferably 5 μm to 20 μm.

11. The rare earth disilicate composition comprises Yb ２ Si ２ O ７ , Er ２ Si ２ O ７ , Lu ２ Si ２ O ７ , or (YbYLuEr) ２ Si ２ O ７ The method according to any one of claims 1 to 10, comprising one of:

12. An environmental barrier coating (EBC) system formed on the surface of a ceramic matrix composite (CMC) to be protected according to the method of any one of claims 1 to 11.

13. The EBC of claim 12 , wherein the CMC comprises a SiC / SiC CMC.

14. further comprising a Si-based bond coat layer directly on the surface of the CMC to be protected; 14. The EBC of claim 12 or 13, wherein the aluminosilicate layer resides directly on the Si-based bond coat layer.

15. The aluminosilicate layer is at least 75 wt. % Al ２ O ３ Al containing ２ O ３ a rare earth disilicate layer having a Yb-rich aluminosilicate composition; ２ Si ２ O ７ , Er ２ Si ２ O ７ , Lu ２ Si ２ O ７ , or (YbYLuEr) ２ Si ２ O ７ The EBC of any one of claims 12 to 14, comprising at least one of the compositions.

16. 1. An environmental barrier coating (EBC) system comprising: an aluminosilicate layer; a rare earth disilicate layer formed on the aluminosilicate layer.

17. The EBC of claim 16 , further comprising a Si-based bond coat layer, wherein the aluminosilicate layer is applied directly onto the Si-based bond coat layer.

18. The aluminosilicate layer is at least 75 wt. % Al ２ O ３ Al containing ２ O ３ 18. The EBC of claim 16 or 17, having a rich aluminosilicate composition.

19. The Al ２ O ３ The rich aluminosilicate composition contains more than 75 wt.% Al ２ O ３ 20. The EBC of claim 18, comprising:

20. The Al ２ O ３ The rich aluminosilicate composition is preferably pure Al ２ O ３ 20. The EBC of claim 18, comprising:

21. The Al ２ O ３ 19. The EBC of claim 18, wherein the rich aluminosilicate layer has a porosity greater than 0% and less than 5% and a thickness in the range of 0.5 μm to 100 μm, preferably 1 μm to 50 μm, more preferably 5 μm to 20 μm.

22. The rare earth disilicate layer is Yb ２ Si ２ O ７ , Er ２ Si ２ O ７ , Lu ２ Si ２ O ７ , or (YbYLuEr) ２ Si ２ O ７ The EBC of any one of claims 16 to 21, comprising at least one of the following compositions:

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