Si-based composite bond coat containing cristobalite modifier for environmental barrier coatings

Abstract

A Si-based composite bond coat for environmental barrier coating on Si-based ceramic matrix composites protects the CMC from oxidizing environments by in-situ modifying the thermally grown oxide (TGO) using a TGO modifier to suppress cristobalite TGO cracking during thermal cycling in gas turbine engines.

Description

Technical Field

[0001] This application claims priority based on U.S. Provisional Application No. 63 / 111,887, filed on November 10, 2020, and U.S. Provisional Application No. 63 / 186,400, filed on May 10, 2021. The entire disclosure of each of these applications is hereby incorporated by reference herein.

[0002] Background of the Invention 1. Field of the Disclosure Example embodiments relate to a bond coat for an environmental barrier coating (EBC) that can protect a Si-based ceramic matrix composite (CMC) in a high-temperature oxidation environment. In particular, example embodiments relate to a silicon-based composite bond coat containing a TGO modifier that suppresses thermally grown oxide (TGO) phase transformation and crack generation during a thermal cycle in a gas turbine engine.

Background Art

[0003] 2. Background Information Environmental barrier coatings (EBCs) have been applied to Si-based ceramic matrix composites to protect CMCs from oxidation and water vapor attack. Current EBC structures consist of a Si bond coat and a protective overlayer such as a rare earth silicate with the general formulas RE2SiO5 (monosilicate) and RE2Si2O7 (disilicate). When the Si bond coat is exposed to the high-temperature oxidizing environment in a gas turbine engine, it oxidizes to form a thermally grown oxide (TGO)SiO2 layer. At high temperatures, upon cooling to approximately 220°C, the silica TGO phase undergoes a first-order displacement transformation from a stable cubic β-cristobalite structure to a tetragonal α-cristobalite. The β-to-α transformation is accompanied by a volume reduction of approximately 4.9%, causing microcracks in the TGO layer. During successive cycles, the TGO microcracks provide fast diffusion pathways for oxidizing agents such as oxygen and water vapor, reaching the Si bond coat surface and accelerating its oxidation rate. Repeated thermal cycling leads to rapid growth and extreme cracking behavior in the TGO layer. This rapid growth causes an increase in the interfacial volume between the topcoat and the bond coat, which generates out-of-plane tensile stress in the EBC system. When the tensile stress exceeds the bonding strength of the coating, fracture occurs. Therefore, a new EBC system with a bond coat capable of preventing the phase transformation of thermally grown SiO2 oxide and the resulting cracking behavior is required for a highly resistant EBC system. [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] overview EBCs can be deposited on Si-based CMC substrates to protect them from oxidation and water vapor attack. In high-temperature gas turbine engine environments, the Si bond coat oxidizes to form a TGO SiO2 layer. During cooling, when cooled to approximately 220°C, the SiO2TGO undergoes a first-order displacement transformation from β-cristobalite to α-cristobalite. This β-to-α transformation is accompanied by a volume reduction of approximately 4.9%, causing microcracks in the TGO layer. As a result of these microcracks, oxide protection is lost, leading to rapid TGO growth and EBC fracture. [Means for solving the problem]

[0005] The Si oxide composite bond coating for EBC on a CMC substrate of this disclosure protects the CMC from oxidation by modifying the TGO layer in situ using a TGO modifier to suppress the occurrence of cristobalite TGO cracks during thermal cycling in a gas turbine engine. Therefore, the Si oxide composite bond coating of this disclosure can significantly improve the lifespan of the CMC component, such as the lifespan of an engine component, in a high-temperature oxidizing environment, and thus improve the lifespan of the engine.

[0006] "TGO modifiers" are defined as rare earth aluminates, oxides containing rare earth oxides, Al2O3, mullite, alkali metal oxides, alkaline earth oxides, alkaline earth silicates, spinel phase AB2O4 (where "A" represents at least one of Mg, Ca, Ba, Sr, or Zn, and "B" represents at least one of Al, Fe, Cr, Co, or V), and mixtures thereof.

[0007] An exemplary embodiment of this disclosure relates to a method for producing bond coats and composite powders on Si-based CMCs. In the exemplary embodiment, the bond coat composite material comprises Si and at least one oxide including at least one rare earth oxide, Al2O3, mullite, alkali metal oxide, alkaline earth oxide, alkaline earth silicate, spinel phase AB2O4 (where "A" represents at least one of Mg, Ca, Ba, Sr, or Zn, and "B" represents at least one of Al, Fe, Cr, Co, or V), and combinations thereof. In the exemplary embodiment, the concentration of Si in the bond coat composite material is in the range of 50 mol% to 99.9 mol%.

[0008] It is preferable to mix at least one oxide having a divalent cation and at least one oxide having a trivalent cation as the mixed oxide in the Si-based composite material. In the example of the embodiment, it is preferable to select a mixture of CaO-Al2O3, SrO-Al2O3, and BaO-Al2O3. In the example of the embodiment, the Si-based composite material is a Si-CaO-Al2O3 composite material in which the CaO / Al2O3 ratio is in the range of 0.1 to 1, and the concentration of the mixed oxide in the Si-CaO-Al2O3 composite material is in the range of 1 to 10 mol%. In the example of another embodiment, the Si-based composite material is a Si-SrO-Al2O3 composite material in which the SrO / Al2O3 ratio is in the range of 0.1 to 1, and the concentration of the mixed oxide in the Si-SrO-Al2O3 composite material is in the range of 1 to 10 mol%. In another embodiment, the Si-based composite material is a Si-BaO-Al2O3 composite material having a BaO / Al2O3 ratio in the range of 0.1 to 1, and the concentration of the mixed oxide in the Si-BaO-Al2O3 composite material is in the range of 1 to 10 mol%.

[0009] The oxide concentration in the Si-based composite material is in the range of 0.01 mol% to 50 mol%. Preferably, the oxide concentration is in the range of 0.1 mol% to 20 mol%. More preferably, the oxide concentration is in the range of 1 mol% to 10 mol%. Preferably, the Si-oxide composite bond coat does not contain boron. During TGO growth at high temperatures, cations of the oxide in the Si-based bond coat diffuse and are incorporated into the β-cristobalite SiO2TGO structure, which stabilizes the β-cristobalite phase and prevents its phase transformation during cooling. Therefore, TGO crack initiation behavior does not occur.

[0010] In some embodiments, the oxide is an alkaline earth oxide, including BeO, MgO, CaO, SrO, BaO, RaO, and combinations thereof. In other embodiments, the oxide is an alkaline earth silicate, including CaO, MgO, and SiO2. In some embodiments, the oxide is an alkali metal oxide, including Li2O, Na2O, K2O, Rb2O, and Cs2O. In other embodiments, the oxide is Rb6O, Rb9O2, CsO, CS3O, CS4O, Cs7O, CS3O2, CS7O2, CS 11 O3, Cs 11 RbO3, Cs 11 Rb2O3, Cs 11 In some embodiments, the oxide is an alkali metal suboxide containing Rb3O3. In some embodiments, the oxide is an alkali metal peroxide containing Li2O2, Na2O2, K2O2, Rb2O2, and Cs2O2. In some embodiments, the oxide is an alkali metal superoxide containing LiO2, NaO2, KO2, RbO2, and CsO2. In other embodiments, the oxide is an alkali metal ozonide containing LiO3, NaO3, KO3, RbO3, and CsO3.

[0011] In a preferred embodiment, the oxide is at least one rare earth oxide, including Y, La, Ce, Pr, Nd, Pm, Sm, Eu, G, Tb, Dy, Ho, Er, Tm, Yb, Lu, and combinations thereof.

[0012] In another example, the bond coat composite material is made of Si and RE3Al5O 12 It consists of at least one rare earth aluminate including REAlO3, RE4Al2O9, and combinations thereof, where RE represents at least one rare earth oxide including Y, La, Ce, Pr, Nd, Pm, Sm, Eu, G, Tb, Dy, Ho, Er, Tm, Yb, Lu, and combinations thereof.

[0013] To prepare a Si-based composite material, it is preferable to mix at least one rare earth aluminate and at least one rare earth oxide in the Si-based composite material. In an example of the embodiment, Y2O3-Y3Al5O 12 Mixture or Yb2O3-Yb3Al5O 12 It is preferable to select the following. The concentration of the mixed oxide in the Si composite material is in the range of 0.01 mol% to 50 mol%, preferably in the range of 0.1 mol% to 20 mol%, and more preferably in the range of 1 mol% to 10 mol%.

[0014] In the embodiment, the concentration of rare earth oxides in the Si-based composite material is in the range of 0.01 mol% to 50 mol%. Preferably, the concentration of rare earth oxides is in the range of 0.1 mol% to 20 mol%. More preferably, the concentration of rare earth oxides is in the range of 1 mol% to 10 mol%. Preferably, the Si-oxide composite bond coat does not contain boron. During TGO growth at high temperatures, cations of rare earth oxides in the Si-based bond coat diffuse and are incorporated into the β-cristobalite SiO2TGO structure, which stabilizes the β-cristobalite phase and prevents its phase transformation during cooling. Therefore, TGO crack initiation behavior does not occur.

[0015] In the embodiment, the rare earth aluminate in the Si-based composite material is in the range of 0.01 mol% to 50 mol%. Preferably, the concentration of the rare earth aluminate is in the range of 0.1 mol% to 20 mol%. More preferably, the concentration of the rare earth aluminate is in the range of 1 mol% to 10 mol%. Preferably, the Si-oxide composite bond coat does not contain boron. During TGO growth at high temperatures, the cations of the rare earth aluminate in the Si-based bond coat diffuse and are incorporated into the β-cristobalite SiO2TGO structure, which stabilizes the β-cristobalite phase and prevents its phase transformation during cooling. Therefore, TGO crack initiation behavior does not occur.

[0016] The Si-oxide composite bond coat of the present disclosure can suppress the cristobalite phase transformation of the TGO layer from cubic to tetragonal during cooling. In addition, the Si-oxide composite bond coat can suppress the crack generation of the TGO layer in a high-temperature oxidation environment. Therefore, the Si-oxide composite bond coat can significantly improve the component life of CMC, such as the engine component life, in a high-temperature oxidation environment, and thus improve the engine life.

[0017] In the following detailed description, the present disclosure will be further described by referring to a plurality of drawings as non-limiting examples of preferred embodiments of the present disclosure.

Brief Description of the Drawings

[0018] [Figure 1] It is a diagram showing a multilayer coating structure having a Si-based composite bond coat according to various embodiments. [Figure 2] It is a diagram showing a scanning electron microscope (SEM) image of the EBC microstructure after a steam test using a conventional Si bond coat according to the prior art. [Figure 3] It is a diagram showing a scanning electron microscope (SEM) image of the EBC microstructure after a steam test using a Si-oxide composite bond coat according to an example of various embodiments.

Modes for Carrying Out the Invention

[0019] Detailed Description FIG. 1 shows a multilayer coating structure 100 having a Si-based composite bond coat 130 according to various embodiments. In FIG. 1, the multilayer coating structure 100 includes a Si-based composite bond coat 130 on a Si-based CMC substrate 140, a high-density airtight Yb2Si2O7 intermediate layer 120 deposited on the Si-based composite bond coat 130, and a calcium-magnesium-aluminosilicate (CMAS) top coat 110 deposited on the high-density airtight Yb2Si2O7 intermediate layer 120.

[0020] Figure 2 shows a SEM image of an EBC microstructure having a Yb2Si2O7 protective top layer, a Si bond coat, and a TGO layer according to the prior art. In Figure 2, the EBC microstructure shows vertical cracks in the TGO layer and horizontal cracks at the interface between the top coat layer and the TGO layer after a steam test at 1316 °C for 215 hours. Upon cooling, a significant volume reduction occurs in the SiO2 TGO layer during its phase transformation from the cubic phase to the tetragonal phase, which results in significant TGO microcracks, loss of oxidation protection properties, and premature failure of the EBC.

[0021] Figure 3 shows a SEM image of an EBC microstructure having a Yb2Si2O7 protective top layer, a bond coat containing Si-5 mol% Al₂O₃, and a TGO layer according to an example of the present disclosure. In Figure 3, the EBC microstructure shows improved EBC resistance, evidenced by the absence of cracks formed in the TGO layer or at the interface between the top coat layer and the TGO layer after a steam test at 1316 °C for 215 hours.

[0022] Si oxide powder can be produced by blending, agglomeration, plasma densification, as well as melting and crushing processes. Si-oxide bond coatings can be deposited by atmospheric plasma spraying (APS: Air Plasma Spray), high velocity oxy-fuel (HVOF: High Velocity Oxy-Fuel), low pressure plasma spraying (LPPS: Low Pressure Plasma Spray), plasma spray - physical vapor deposition (PS-PVD: Plasma Spray-Physical Vapor Deposition), chemical vapor deposition (CVD: Chemical Vapor Deposition), physical vapor deposition (PVD: Physical Vapor Deposition), electron beam - physical vapor deposition (EB-PVD: Electron Beam-Physical Vapor Deposition), suspension / solution plasma spraying (SPS: Suspension / Solution Plasma Spray), suspension / solution HVOF (S-HVOF), and slurry processes.

[0023] Furthermore, since the present invention is disclosed herein in a manner that allows for the invention to be made and used from the disclosure of embodiments as specific examples, for example for simplicity or efficiency, the present invention can be carried out without any additional elements or structures not specifically disclosed herein.

[0024] The above examples are provided for illustrative purposes only and should not be construed as limiting the invention. Although the invention has been described with reference to specific embodiments, it should be understood that the words used herein are descriptive and illustrative, not limiting. Modifications may be made within the scope of the currently described and amended appendix claims without departing from the scope and spirit of the aspects of the invention. Although the invention has been described herein with reference to specific means, materials and embodiments, the invention is not intended to be limited to the details disclosed herein, but rather extends to all functionally equivalent structures, methods and uses, for example, within the scope of the appendix claims.

Claims

1. An environmental barrier coating (EBC) structure on a Si-based ceramic matrix composite (CMC), The aforementioned environmental barrier coating (EBC) structure is Si-based composite bond coating, The cristobalite thermally grown oxide (TGO) layer on the Si-based composite bond coat, The cristobalite thermally grown oxide (TGO) layer comprises a rare earth silicate protective upper layer, The aforementioned Si-based composite bond coat is Si in a concentration range of 50 mol% to 99.9 mol%, The invention comprises a thermally grown oxide (TGO) modifier that suppresses crack formation in the cristobalite thermally grown oxide (TGO) layer during the thermal cycle in a gas turbine engine, The aforementioned thermally grown oxide (TGO) modifier is Al ２ O ３ 、 a combination of Al ２ O ３ and an alkali metal oxide, a combination of Al ２ O ３ and an alkaline earth metal oxide, a spinel phase AB ２ O ４ 、 and Al ２ O ３ and a spinel phase AB ２ O ４ and includes at least one oxide selected from the group consisting of a combination with A represents at least one of Mg, Ca, Ba, Sr, or Zn, and B represents at least one of Al, Fe, Cr, Co, or V. The cristobalite thermally grown oxide (TGO) layer comprises β-cristobalite SiO2 and the cation of at least one of the oxides. Environmental barrier coating (EBC) structure.

2. The environmental barrier coating (EBC) structure according to claim 1, wherein the at least one oxide includes a mixed oxide obtained by mixing at least one first oxide having a divalent cation and at least one second oxide having a trivalent cation.

3. The aforementioned Si-based composite bond coating is CaO / Al ２ O ３ Si-CaO-Al with a ratio in the range of 0.1 to 1 ２ O ３ It is a composite material, and the Si-CaO-Al ２ O ３ The environmental barrier coating (EBC) structure according to claim 2, wherein the mixed oxide in the composite material is in the range of 1 mol% to 10 mol%.

4. The aforementioned Si-based composite bond coating is SrO / Al ２ O ３ Si-SrO-Al with a ratio in the range of 0.1 to 1 ２ O ３ It is a composite material, and the Si-SrO-Al ２ O ３ The environmental barrier coating (EBC) structure according to claim 2, wherein the mixed oxide in the composite material is in the range of 1 mol% to 10 mol%.

5. The Si-based composite bond coating is BaO / Al ２ O ３ Si-BaO-Al with a ratio in the range of 0.1 to 1 ２ O ３ It is a composite material, and the Si-BaO-Al ２ O ３ The environmental barrier coating (EBC) structure according to claim 2, wherein the mixed oxide in the composite material is in the range of 1 mol% to 10 mol%.

6. An environmental barrier coating (EBC) structure on a Si-based ceramic matrix composite (CMC), The aforementioned environmental barrier coating (EBC) structure is Si-based composite bond coating, The cristobalite thermally grown oxide (TGO) layer on the Si-based composite bond coat, The TGO layer comprises a rare earth silicate protective upper layer, The aforementioned Si-based composite bond coat is Si in a concentration range of 50 mol% to 99.9 mol%, The invention comprises a thermally grown oxide (TGO) modifier that suppresses crack formation in the cristobalite thermally grown oxide (TGO) layer during the thermal cycle in a gas turbine engine, The aforementioned thermally grown oxide (TGO) modifier is At least one rare-earth aluminate, Al ２ O ３ Al ２ O ３ and alkali metal oxide combination, Al ２ O ３ and the combination with alkaline earth oxides, spinel phase AB ２ O ４ , and Al ２ O ３ and spinel phase AB ２ O ４ It comprises at least one oxide selected from the group consisting of combinations of the following, A represents at least one of Mg, Ca, Ba, Sr, or Zn, and B represents at least one of Al, Fe, Cr, Co, or V. The cristobalite thermally grown oxide (TGO) layer comprises β-cristobalite SiO2 and cations of at least one rare earth aluminate or at least one oxide. Environmental barrier coating (EBC) structure.

7. A method for preparing a Si-based composite bond coat used to manufacture an environmental barrier coating (EBC) structure according to claim 6, wherein the method is: The process includes the step of combining at least one rare earth aluminate and at least one oxide, wherein the at least one oxide is Al ２ O ３ Al ２ O ３ and alkali metal oxide combination, Al ２ O ３ and the combination with alkaline earth oxides, spinel phase AB ２ O ４ , and Al ２ O ３ and spinel phase AB ２ O ４ Selected from the group consisting of combinations of, A method in which A represents at least one of Mg, Ca, Ba, Sr, or Zn, and B represents at least one of Al, Fe, Cr, Co, or V.

8. The environmental barrier coating (EBC) structure according to claim 6, wherein the concentration of at least one rare earth aluminate is in the range of 0.01 mol% to 50 mol%.

9. The environmental barrier coating (EBC) structure according to claim 6, wherein the concentration of at least one rare earth aluminate is in the range of 0.1 mol% to 20 mol%.

10. The environmental barrier coating (EBC) structure according to claim 6, wherein the concentration of at least one rare earth aluminate is in the range of 1 mol% to 10 mol%.

11. The environmental barrier coating (EBC) structure according to claim 6, wherein the concentration of the combination of at least one rare earth aluminate and at least one oxide is in the range of 0.01 mol% to 50 mol%.

12. The environmental barrier coating (EBC) structure according to claim 6, wherein the concentration of the combination of the at least one rare earth aluminate and the at least one oxide is in the range of 0.1 mol% to 20 mol%.

13. The environmental barrier coating (EBC) structure according to claim 6, wherein the concentration of the combination of the at least one rare earth aluminate and the at least one oxide is in the range of 1 mol% to 10 mol%.

14. A method for providing an environmental barrier coating (EBC) structure according to claim 1 on a Si-based CMC, wherein the method is: A method comprising the step of depositing the Si-based composite bond coat described in claim 1 onto the Si-based CMC.

15. The method according to claim 14, wherein the deposition step is carried out by a chemical deposition process, a physical deposition process, atmospheric plasma spraying (APS), a slurry process, suspension / solution plasma spraying (SPS), low-pressure plasma spraying (LPPS), high-velocity oxygen fuel (HVOF), or an aerosol deposition process.

16. An environmental barrier coating (EBC) structure according to claim 1 or claim 6 in a thermal cycle of a gas turbine engine.

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