SI-BASED COMPOSITE BOND COAT CONTAINING CRISTOBALITE MODIFIER FOR ENVIRONMENTAL BARRIER COATINGS

Abstract

A Si-based composite bond coat for environmental barrier coatings on a Si-based ceramic matrix composite that protects the CMC from an oxidation environment by in-situ modifying a thermally grown oxide (TGO) using a TGO modifier to suppress cristobalite TGO cracking during thermal cycling in a gas turbine engine.

Claims

1. A Si-based composite bond coat for environmental barrier coatings (EBCs) on a Si-based ceramic matrix composite (CMC) comprising: a thermally grown oxide (TGO) modifier that suppresses cristobalite TGO cracking during thermal cycling in a gas turbine engine, and at least one oxide selected from the group consisting of Al.sub.2O.sub.3, a combination of Al.sub.2O.sub.3 and an alkali metal oxide, a combination of Al.sub.2O.sub.3 and an alkaline earth oxide, a spinel phase AB.sub.2O.sub.4, and a combination of Al.sub.2O.sub.3 and the spinel phase AB.sub.2O.sub.4, wherein 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.

2. The Si-based composite bond coat according to claim 1, wherein said Si-based composite bond coat comprises: Si in a concentration range of 50 mol % to 99.9 mol %.

3. The Si-based composite bond coat according to claim 1, wherein the at least one oxide comprises mixed oxides that are obtained by mixing at least one first oxide with two valence cations and at least a second oxide with three valence cations.

4. The Si-based composite bond coat according to claim 3, wherein the Si-based composite bond coat is a Si—CaO—Al.sub.2O.sub.3 composite having a ratio of CaO/Al.sub.2O.sub.3 in a range of 0.1-1, and wherein the mixed oxides in the Si—CaO—Al.sub.2O.sub.3 composite are in a range of 1 mol % to 10 mol %.

5. The Si-based composite bond coat according to claim 3, wherein the Si-based composite bond coat is a Si—SrO—Al.sub.2O.sub.3 composite having a ratio of SrO/Al.sub.2O.sub.3 in a range of 0.1-1, and wherein the mixed oxides in the Si—SrO—Al.sub.2O.sub.3 composite are in a range of 1 mol % to 10 mol %.

6. The Si-based composite bond coat according to claim 3, wherein the Si-based composite bond coat is a Si—BaO—Al.sub.2O.sub.3 composite having a ratio of BaO/Al.sub.2O.sub.3 in a range of 0.1-1, and wherein the mixed oxides in the Si—BaO—Al.sub.2O.sub.3 composite are in a range of 1 mol % to 10 mol %.

9. A Si-based composite bond coat comprising: at least one rare earth aluminate; and at least one oxide selected from the group consisting of Al.sub.2O.sub.3, a combination of Al.sub.2O.sub.3 and an alkali metal oxide, a combination of Al.sub.2O.sub.3 and an alkaline earth oxide, a spinel phase AB.sub.2O.sub.4, and a combination of Al.sub.2O.sub.3 and the spinel phase AB.sub.2O.sub.4, wherein 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.

10. A method of preparing a Si-based composite bond coat, comprising: combining at least one rare earth aluminate and at least one oxide selected from the group consisting of Al.sub.2O.sub.3, a combination of Al.sub.2O.sub.3 and an alkali metal oxide, a combination of Al.sub.2O.sub.3 and an alkaline earth oxide, a spinel phase AB.sub.2O.sub.4, and a combination of Al.sub.2O.sub.3 and the spinel phase AB.sub.2O.sub.4, wherein 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 to form a mixture.

14. The Si-based composite bond coat according to claim 8, wherein the at least one rare earth aluminate concentration is in a range of 0.01 mol % to 50 mol %.

15. The Si-based composite bond coat according to claim 8, wherein the at least one rare earth aluminate concentration is in a range of 0.1 mol % to 20 mol %.

16. The Si-based composite bond coat according to claim 8, wherein the at least one rare earth aluminate concentration is in a range of 1 mol % to 10 mol %.

17. The Si-based composite according to claim 9, wherein a combination of the at least one rare earth aluminate concentration and the at least one oxide concentration is in a range of 0.01 mol % to 50 mol %.

18. The Si-based composite according to claim 9, wherein a combination of the at least one rare earth aluminate concentration and the at least one oxide concentration is in a range of 0.1 mol % to 20 mol %.

19. The Si-based composite according to claim 9, wherein a combination of the at least one rare earth aluminate concentration and the at least one oxide concentration is in a range of 1 mol % to 10 mol %.

20. A method of applying a bond coat on a Si-based CMC, comprising: depositing the Si-based composite bond coat of claim 1 on the Si-based CMC.

21. The method according to claim 15, wherein the depositing is performed by a chemical vapor deposition process, a physical vapor deposition process, Air Plasma Spray (APS), a slurry process, Suspension/Solution Plasma Spray (SPS), Low Pressure Plasma Spray (LPPS), High Velocity Oxy-Fuel (HVOF), or an aerosol deposition process.

22. Use of a TGO modifier to suppress cristobalite TGO during thermal cycling in a gas turbine engine, wherein said TGO modifier is a rare earth aluminate, or an oxide, wherein said oxide is at least one selected from the group consisting of Al.sub.2O.sub.3, a combination of Al.sub.2O.sub.3 and an alkali metal oxide, a combination of Al.sub.2O.sub.3 and an alkaline earth oxide, a spinel phase AB.sub.2O.sub.4, and a combination of Al.sub.2O.sub.3 and the spinel phase AB.sub.2O.sub.4, wherein “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.

23. The Si-based composite bond coat according to claim 2, wherein said Si is in a concentration range of 87 mol % to 99.9 mol %.

24. The Si-based composite bond coat according to claim 2, wherein said Si is in a concentration range of 92 mol % to 96 mol %.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present disclosure is further described in the detailed description which follows, in reference to the noted plurality of drawings, by way of non-limiting examples of preferred embodiments of the present disclosure.

[0018] FIG. 1 illustrates a multilayer coating structure having a Si-based composite bond coat, according to various embodiments.

[0019] FIG. 2 illustrates a scanning electron microscope (SEM) image of an EBC microstructure after a steam test using a conventional Si bond coat, according to the prior art.

[0020] FIG. 3 illustrates a scanning electron microscope (SEM) image of an EBC microstructure after a steam test using a Si-oxide composite bond coat, according to various example embodiments.

DETAILED DESCRIPTION

[0021] FIG. 1 illustrates 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 the Si-based CMC substrate 140, a dense and hermetic Yb.sub.2Si.sub.2O.sub.7 intermediate layer 120 deposited on the Si-based composite bond coat 130, and a calcium-magnesium-aluminosilicate (CMAS) resistant topcoat 110 deposited on the dense and hermetic Yb.sub.2Si.sub.2O.sub.7 intermediate layer 120.

[0022] FIG. 2 illustrates a SEM image of an EBC microstructure having a Yb.sub.2Si.sub.2O.sub.7 protective top layer, a Si bond coat, and a TGO layer, according to the prior art. In FIG. 2, the EBC microstructure shows a vertical crack in the TGO layer and horizontal cracks between the interface of the topcoat layer and the TGO layer after conducting a steam test at 1316° C. for 215 hours. Upon cooling, the SiO.sub.2 TGO layer underwent a large volume reduction during its cubic to tetragonal phase transformation, resulting in severe TGO microcracking, loss of oxidation protection properties, and premature spallation of the EBCs.

[0023] FIG. 3 illustrates a SEM image of an EBC microstructure having a Yb.sub.2Si.sub.2O.sub.7 protective top layer, a bond coat including Si-5 mol % Al.sub.2O.sub.3, and a TGO layer, according to an example of the present disclosure. In FIG. 3, the EBC microstructure shows improved EBC durability as evidenced by no crack formations in the TGO layer or at the interface of the topcoat layer and the TGO layer after conducting a steam test at 1316° C. for 215 hours.

[0024] The Si-oxide powders can be manufactured by blend, agglomeration, plasma densification, and fused and crushed processes. The Si-oxide bond coatings may be deposited by Air Plasma Spray (APS), High Velocity Oxy-Fuel (HVOF), Low Pressure Plasma Spray (LPPS), Plasma Spray-Physical Vapor Deposition (PS-PVD), Chemical Vapor Deposition (CVD), Physical Vapor Deposition (PVD), Electron Beam-Physical Vapor Deposition (EB-PVD), Suspension/Solution Plasma Spray (SPS), Suspension/Solution HVOF (S-HVOF), and a slurry process.

[0025] Further, at least because the invention is disclosed herein in a manner that enables one to make and use it, by virtue of the disclosure of particular exemplary embodiments, such as for simplicity or efficiency, for example, the invention can be practiced in the absence of any additional element or additional structure that is not specifically disclosed herein.

[0026] It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to an exemplary embodiment, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. Although the present invention has been described herein with reference to particular means, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims.