Alumina-rich aluminosilicate diffusion barrier 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. The method comprises applying an aluminosilicate composition on the surface of the CMC to be protected to form an aluminosilicate layer; and applying a rare earth disilicate composition to the aluminosilicate layer.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This international application claims the benefit / priority of U.S. Provisional Application No. 63 / 405,025, filed on September 9, 2022, the disclosure of which is expressly incorporated herein by reference in its entirety. Technical Field

[0003] Embodiments are directed to methods of forming environmental barrier coatings (EBCs) needed to protect SiC-based ceramic matrix composite (CMC) components from water vapor corrosion, and to the structures of EBCs formed by such methods. Background Art

[0004] Environmental barrier coatings (EBCs) have been applied to Si-based CMCs to protect the CMCs from oxidation and water vapor corrosion. Current EBC systems consist of a silicon bond coat applied to the surface of the SiC CMC substrate to be protected, followed by one or more rare earth disilicate (e.g., Yb2Si2O7) protective coatings (as top coats). It is known that during the service life of CMC components, oxidants, such as water vapor and oxygen, can diffuse through the EBC layer and oxidize the Si-based bond coat, which results in the growth of a cristobalite SiO2 thermally grown oxide (TGO) layer. This cristobalite SiO2 TGO growth is the main cause of failure of environmental barrier coatings (EBCs). When the thermally grown oxide (TGO) reaches a threshold thickness, this EBC will flake off. Therefore, it is important to slow down the TGO growth rate and improve the durability of the EBC coating. Summary of the invention

[0005] Embodiments relate to a method for forming an environmental barrier coating (EBC) system, which includes applying a low oxidation diffusion barrier layer between a rare earth disilicate layer and a Si-based bond coat to reduce the rate of undesirable TGO growth. The low oxidation diffusion barrier layer specifically includes an Al2O3-rich aluminosilicate composition, for example, the Al2O3 weight percentage can be 75-100%, preferably 77%-87% Al2O3, and the rest is SiO2. There are two reasons for selecting an Al2O3-rich aluminosilicate:

[0006] 1) Al2O3-rich aluminosilicates have low oxidation diffusion coefficients, which can slow down the diffusion of oxidants; and

[0007] 2) Excess Al2O3, i.e., Al2O3 content >75% in Al2O3-rich aluminosilicates, can react with cristobalite SiO2 TGO to form two phases - Al2O3 + mullite phase, thereby changing the TGO chemistry and avoiding cristobalite SiO2 phase transformation during thermal cycling.

[0008] In order to reduce the TGO growth rate in the EBC, a low oxidant / oxidation diffusion barrier layer is formed between the rare earth disilicate layer on the substrate (preferably the surface of the CMC component) and the Si-based bond coat. The oxidation diffusion barrier layer includes an Al2O3-rich aluminosilicate composition, which has a low oxidant / oxidation diffusion coefficient and can slow down the diffusion of oxidants. In addition, since excess Al2O3 can react with cristobalite SiO2 TGO to form a mullite phase, the TGO chemistry can be changed to avoid cristobalite SiO2 phase transformation during thermal cycling.

[0009] According to the embodiment, water vapor testing of EBCs at 1400°C for 170 hours and 410 hours showed that TGO growth in multilayer EBCs (i.e., EBCs with Al2O3-rich aluminosilicate as the middle layer) was about 3 times slower than that in conventional EBCs (i.e., without Al2O3-rich aluminosilicate middle layer).

[0010] The Al2O3-rich aluminosilicate coating can be deposited by: air plasma spraying; low pressure plasma spraying; high velocity oxygen fuel spraying; suspension thermal spraying; slurry coating process; chemical vapor deposition; or physical vapor deposition. In addition, for thermal spraying, the Al2O3-rich aluminosilicate raw material powder can be: melted / crushed; spray dried; agglomerated and sintered; or plasma densified. The Al2O3-rich aluminosilicate raw material powder can have a particle size range between 11 μm and 105 μm, preferably between 11 μm and 62 μm.

[0011] According to an embodiment, the Al2O3-rich aluminosilicate coating formed in the multilayer EBC has a porosity greater than 0% and less than 5%, and a thickness ranging from 0.5 μm to 100 μm, preferably between 1-50 μm, and more preferably between 5-20 μm.

[0012] 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 includes applying an aluminosilicate composition to the surface of the CMC to be protected to form an aluminosilicate layer; and applying a rare earth disilicate composition to the aluminosilicate layer.

[0013] In an embodiment, the CMC may include a SiC / SiC CMC.

[0014] According to other embodiments, the method may further comprise applying a Si-based bond coating directly onto the surface of the CMC to be protected. The aluminosilicate layer is applied directly onto the Si-based bond coating.

[0015] According to an embodiment, the aluminosilicate composition may include an aluminosilicate composition rich in Al2O3, the aluminosilicate composition rich in Al2O3 includes at least 75wt% Al2O3, and the aluminosilicate layer includes an aluminosilicate layer rich in Al2O3. The aluminosilicate composition rich in Al2O3 may include more than 75wt% Al2O3. Further, the aluminosilicate composition rich in Al2O3 may include pure Al2O3. The aluminosilicate layer rich in Al2O3 may be formed by one of the following methods: thermal spray deposition, slurry coating process, chemical vapor deposition or physical vapor deposition. Further, when the aluminosilicate layer rich in Al2O3 is formed by thermal spray deposition, the aluminosilicate raw material rich in Al2O3 may include molten / crushed particles, spray-dried particles, agglomerated and sintered particles, or plasma densified particles. The particle size range of the aluminosilicate raw material rich in Al2O3 may be 11μm-105μm, preferably 11μm-62μm. The porosity of the Al2O3-rich aluminosilicate layer may be greater than 0% and less than 5%, and the thickness may range from 0.5 μm to 100 μm, preferably between 1 μm and 50 μm, and more preferably between 5 μm and 20 μm.

[0016] According to other embodiments, the rare earth disilicate composition includes: Yb2Si2O7, Er2Si2O7, Lu2Si2O7 or (YbYLuEr)2Si2O7.

[0017] Embodiments relate to an environmental barrier coating (EBC) system formed on a surface of a ceramic matrix composite (CMC) to be protected according to the above method.

[0018] According to an embodiment, the CMC may include a SiC / SiC CMC.

[0019] According to other embodiments, the EBC may further comprise a Si-based bond coating directly on the surface of the CMC to be protected. The aluminosilicate layer may be applied directly onto the Si-based bond coating.

[0020] In other embodiments, the aluminosilicate layer may have an Al2O3-rich aluminosilicate composition, the Al2O3-rich aluminosilicate composition including at least 75wt% Al2O3, and the rare earth disilicate layer may include: Yb2Si2O7, Er2Si2O7, Lu2Si2O7 or (YbYLuEr)2Si2O7 composition.

[0021] Embodiments relate to an environmental barrier coating (EBC) system including: an aluminosilicate layer; and a rare earth disilicate layer formed on the aluminosilicate layer.

[0022] According to an embodiment, the EBC may further include a Si-based bond coating, and the aluminosilicate layer may be directly applied to the Si-based bond coating.

[0023] In other embodiments, the aluminosilicate layer may have an Al2O3-rich aluminosilicate composition, the Al2O3-rich aluminosilicate composition comprising at least 75 wt% Al2O3. The Al2O3-rich aluminosilicate composition may include more than 75 wt% Al2O3. Further, the Al2O3-rich aluminosilicate composition may include 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 between 1 μm and 50 μm, and more preferably between 5 μm and 20 μm.

[0024] According to other embodiments, the rare earth disilicate layer may include: Yb2Si2O7, Er2Si2O7, Lu2Si2O7 or a (YbYLuEr)2Si2O7 combination.

[0025] Other exemplary embodiments and advantages of the present invention can be ascertained from a review of the disclosure and accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In the following detailed description, the invention is further described by way of non-limiting examples of exemplary embodiments of the invention with reference to the accompanying drawings in which like reference numerals represent similar parts throughout the several views, and in which:

[0027] Figure 1A and 1B Schematically illustrates a multi-layer EBC according to an embodiment;

[0028] Figure 2 The phase diagram of Al2O3-SiO2 is shown;

[0029] Figure 3 shows the diffusion coefficient of oxygen as a function of temperature;

[0030] Figures 4A-4C It shows that the known EBC ( Figure 4A ) and the EBC according to the embodiment ( Figure 4B , 4C )’s microstructure SEM image;

[0031] Figures 5A-5C It shows that the known EBC ( Figure 5A ) and the EBC evaluated at 1400°C for 170 hours in 90 vol% H2O-10 vol% air according to the embodiment ( Figure 5B , 5C ) in TGO growth behavior; and

[0032] Figures 6A-6C It shows that the known EBC ( Fig. 6A ) and the EBC evaluated at 1400°C for 410 hours in 90 vol% H2O-10 vol% air according to the embodiment ( Figure 6B , 6C ) in the TGO growth behavior. DETAILED DESCRIPTION

[0033] The details shown herein are presented by way of example only for the purpose of illustrative discussion of embodiments of the present invention, and are presented in order to provide what is considered to be the most useful and most easily understood description of the principles and concepts of the present invention. In this regard, no attempt is made to show the structural details of the present invention in more detail than is necessary for a basic understanding of the present invention, and the description in conjunction with the accompanying drawings makes it clear to those skilled in the art how several forms of the present invention can be embodied in practice.

[0034] A coating system, particularly an EBC coating system having an Al2O3-rich aluminosilicate composition layer, is deposited onto the surface of a SiC / SiC ceramic matrix composite (CMC) component or onto a Si-based bond coat in a multilayer EBC system. The Al2O3-rich aluminosilicate coating can slow down oxidant diffusion and significantly reduce TGO growth rate, while excess Al2O3 in the Al2O3-rich aluminosilicate coating can consume growing SiO2 TGO and react with growing SiO2 TGO, thereby changing TGO growth behavior. For example, the Al2O3 concentration in the Al2O3-rich aluminosilicate composition is greater than 75 wt%, with the remainder being SiO2.

[0035] TGO growth depends significantly on the composition, microstructure and architecture of the coating material. In order 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 bonding coating, which can slow down the oxidant diffusion. In an embodiment, the oxidation diffusion barrier layer may include an Al2O3-rich aluminosilicate composition. The Al2O3-rich aluminosilicate layer of the oxidation diffusion barrier layer is advantageous because the Al2O3-rich aluminosilicate has a low oxidant diffusion coefficient, which can slow down the oxidant diffusion. In addition, the excess Al2O3 in the Al2O3-rich aluminosilicate coating can react with the quartz SiO2 TGO to form a mullite phase, which can change the TGO chemistry and avoid the quartz SiO2 phase transition during thermal cycling.

[0036] Figure 1A and 1B An exemplary embodiment of an EBC coating system 1 , 1 ′ formed on a SiC CMC component 2 is shown. Figure 1A The invention is a three-layer EBC coating system, which includes a rare earth disilicate layer 3 (such as Yb2Si2O7, Er2Si2O7, Lu2Si2O7, (YbYLuEr)2Si2O7, etc.) formed on an Al2O3-rich aluminosilicate layer 4, and a Si-based bonding coating 5 applied to a SiC CMC 2. Figure 1B In the embodiment, the two-layer EBC coating system 1' includes a rare earth disilicate layer 3 (e.g., Yb2Si2O7, Er2Si2O7, Lu2Si2O7, (YbYLuEr)2Si2O7, etc.) formed on an Al2O3-rich aluminosilicate layer 4, which is applied to a SiC CMC (or SiC / SiC CMC) 2 with a Si-based bonding coating. In some applications, the double-layer EBC coating system 1' can be used without a Si-based bonding coating, so that the alumina-rich aluminosilicate can be directly applied to the SiC / SiC CMC to protect the CMC. In addition, since the SiC surface will be oxidized to form a SiO2 TGO layer, the alumina-rich aluminosilicate will slow down the TGO growth rate. Further, since the melting point of silicon is about 1414°C, the double-layer EBC coating system 1' can be advantageous in a high temperature environment greater than 1400°C.

[0037] The Al2O3-rich aluminosilicate coating of the EBC coating system 1, 1' can be formed by the following methods: thermal spray deposition (including air plasma spray deposition, low-pressure plasma spray deposition, high-velocity oxygen-fuel spray deposition and suspension thermal spray deposition), slurry coating process, chemical vapor deposition or physical vapor deposition. In addition, when the intermediate coating is applied by one of the thermal spray deposition processes, the Al2O3-rich aluminosilicate raw material powder can be made of the following particles: molten / crushed particles, spray-dried particles, agglomerated and sintered particles or plasma densified particles. The particle size range of the Al2O3-rich aluminosilicate raw material is 11μm to 105μm, preferably between 11μm and 62μm.

[0038] The Al2O3-rich aluminosilicate intermediate coating in the EBC coating system 1, 1' may have a porosity greater than 0% and less than 5%, a thickness ranging from 0.5 μm to 100 μm, preferably between 1 μm and 50 μm, and more preferably between 5 μm and 20 μm.

[0039] Figure 2The phase diagram of Al2O3-SiO2 is shown, 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). Figure 2 It can be seen that the Al2O3-rich aluminosilicate material (formed by Figure 1A and 1B The Al2O3-rich aluminosilicate layer 3) comprises an excess of aluminum oxide compared to the stoichiometric mullite, for example, an Al2O3 content greater than 75 wt%. It has been found that this excess Al2O3 reacts with and consumes SiO2 TGO, thus changing the TGO growth behavior. In addition, 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). Figure 3 As shown, Al2O3 and mullite have low oxygen diffusion coefficients compared to other compositions.

[0040] Figure 4A SEM images showing the microstructure of a known double-layer EBC system consisting of a rare earth disilicate layer (such as Yb2Si2O7, Er2Si2O7, Lu2Si2O7, (YbYLuEr)2Si2O7, etc.) and a Si-based bonding coating. Figure 5A Show Figure 4A The growth behavior of TGO (~6.9 μm) on Si-based bond coating was evaluated in a 90 vol% H2O-10 vol% air environment at 1400°C for 170 h for a known double-layer EBC system. Fig. 6A Show Figure 4A The sustained growth behavior of TGO (~9.2 μm) on Si-based bond coatings of a known double-layer EBC system was evaluated in a 90 vol% H2O-10 vol% air environment at 1400°C for 410 h.

[0041] In an exemplary embodiment, although an extreme example, Figure 4BAn SEM image showing the microstructure of a three-layer EBC system including a rare earth disilicate layer (such as Yb2Si2O7, Er2Si2O7, Lu2Si2O7, (YbYLuEr)2Si2O7, etc.), an Al2O3-rich aluminosilicate composition layer (i.e., a pure Al2O3 intermediate layer (without SiO2)) and a Si-based bonding coating. Figure 5B Show Figure 4B The growth behavior of TGO (~1.7 μm) on Si-based bond coatings evaluated in an EBC system in a 90 vol% H2O-10 vol% air environment at 1400°C for 170 hours. In addition, since this pure Al2O3 composition has an Al2O3 concentration of more than 75 wt% (the remainder is SiO2) in an Al2O3-rich aluminosilicate composition, this excess Al2O3 is able to consume and react with the growing SiO2 TGO, thus changing the TGO growth behavior. Figure 5B As shown, it can be seen that due to this reaction between Al2O3 and SiO2, the excess Al2O3 in the intermediate layer, that is, more than 75wt% of Al2O3, is converted into the mullite phase. Figure 6B show when Figure 4B The sustained growth behavior of TGO (~2.7 μm) on Si-based bond coatings evaluated by the EBC system in a 90 vol% H2O-10 vol% air environment at 1400°C for 410 h, and the ability to Figure 6B An additional mullite phase is observed in the Al2O3 interlayer in the MgO2 matrix, which is produced by the continuous reaction between Al2O3 and SiO2, where SiO2 TGO will diffuse upward into the Al2O3 interlayer to react with Al2O3.

[0042] In another exemplary embodiment, Figure 4C The SEM image of the microstructure of a three-layer EBC system is shown, which includes a rare earth disilicate layer (such as Yb2Si2O7, Er2Si2O7, Lu2Si2O7, (YbYLuEr)2Si2O7, etc.), an Al2O3-rich aluminosilicate composition layer (i.e., alumina-mullite composed of 77wt% Al2O3-23wt% SiO2) and a Si-based bonding coating. Figure 5C show when Figure 4C The growth behavior of TGO (~1.8 μm) on Si-based bond coatings was evaluated in an EBC system in a 90 vol% H2O-10 vol% air environment at 1400°C for 170 h. Figure 6C show when Figure 4CThe sustained growth behavior of TGO (~3.5 μm) on Si-based bond coatings was evaluated in an EBC system in a 90 vol% H2O-10 vol% air environment at 1400°C for 410 h.

[0043] Therefore, it is obvious that Figure 4A (as well as Figure 5A and 6A ) compared to EBC without Al2O3-rich aluminosilicate layer. Figure 4B (as well as Figure 5B and 6B )and Figure 4C (as well as Figure 5C and 6C ) The above-mentioned exemplary embodiment with an Al2O3-rich aluminosilicate intermediate layer is very effective in slowing down the TGO growth rate in the EBC.

[0044] It is noteworthy that the foregoing embodiments are provided for the purpose of explanation only and are in no way to be construed as limiting the present invention. Although the present invention has been described with reference to exemplary embodiments, it should be understood that the words used herein are words of description and illustration, rather than words of limitation. Without departing from the scope and spirit of the present invention, changes may be made within the scope of the appended claims, as currently described and modified. Although the present invention has been described herein with reference to specific modes, materials, and embodiments, the present invention is not intended to be limited to the details disclosed herein; on the contrary, the present invention extends to all functionally equivalent structures, methods, and uses, such as within the scope of the appended claims.

Claims

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 on the surface of the CMC to be protected to form an aluminosilicate layer; and A rare earth disilicate composition is applied to the aluminosilicate layer.

2. The method according to claim 1, wherein: The CMC includes a SiC / SiC CMC.

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

4. The method according to any one of claims 1 to 3, wherein: The aluminosilicate composition comprises an Al2O3-rich aluminosilicate composition, the Al2O3-rich aluminosilicate composition comprising at least 75 wt% Al2O3, and The aluminosilicate layer includes an Al2O3-rich aluminosilicate layer.

5. The method according to claim 4, wherein: The Al2O3-rich aluminosilicate composition comprises more than 75 wt% Al2O3.

6. The method according to claim 4, wherein: The Al2O3-rich aluminosilicate composition comprises pure Al2O3.

7. The method according to claim 4, wherein: The Al2O3-rich aluminosilicate layer is formed by one of the following methods: thermal spray deposition, slurry coating process, chemical vapor deposition or physical vapor deposition.

8. The method according to claim 7, wherein: When the Al2O3-rich aluminosilicate layer is formed by thermal spray deposition, the Al2O3-rich aluminosilicate raw material includes: molten / pulverized particles, spray-dried particles, agglomerated and sintered particles, or plasma densified particles.

9. The method according to claim 8, wherein: The particle size of the Al2O3-rich aluminosilicate raw material ranges from 11 μm to 105 μm, preferably from 11 μm to 62 μm.

10. The method according to claim 4, wherein: The porosity of the Al2O3-rich aluminosilicate layer is greater than 0% and less than 5%, and the thickness ranges from 0.5 μm to 100 μm, preferably between 1 μm and 50 μm, and more preferably between 5 μm and 20 μm.

11. The method according to any one of claims 1 to 10, wherein: The rare earth disilicate composition includes: Yb2Si2O7, Er2Si2O7, Lu2Si2O7 or (YbYLuEr)2Si2O7.

12. An environmental barrier coating (EBC) system formed on a 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 according to claim 12, wherein: The CMC includes a SiC / SiC CMC.

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

15. The EBC according to any one of claims 12 to 14, wherein: The aluminosilicate layer has an Al2O3-rich aluminosilicate composition, the Al2O3-rich aluminosilicate composition includes at least 75wt% Al2O3, and the rare earth disilicate layer includes at least one of Yb2Si2O7, Er2Si2O7, Lu2Si2O7 or (YbYLuEr)2Si2O7 compositions.

16. An environmental barrier coating (EBC) system comprising: Aluminosilicate layer; and A rare earth disilicate layer is formed on the aluminosilicate layer.

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

18. The EBC according to claim 16 or 17, wherein: The aluminosilicate layer has an Al2O3-rich aluminosilicate composition comprising at least 75 wt% Al2O3.

19. The EBC of claim 18, wherein: The Al2O3-rich aluminosilicate composition comprises more than 75 wt% Al2O3.

20. The EBC of claim 18, wherein: The Al2O3-rich aluminosilicate composition comprises pure Al2O3.

21. The EBC of claim 18, wherein: The porosity of the Al2O3-rich aluminosilicate layer is greater than 0% and less than 5%, and the thickness ranges from 0.5 μm to 100 μm, preferably between 1 μm and 50 μm, and more preferably between 5 μm and 20 μm.

22. The EBC according to any one of claims 16-21, wherein The rare earth disilicate layer includes at least one of Yb2Si2O7, Er2Si2O7, Lu2Si2O7 or a (YbYLuEr)2Si2O7 composition.

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