We claim:
1. An environmental barrier coating system for a component of a gas turbine,
comprising:
at least one rare earth disilicate layer; and at least one rare earth monosilicate layer, wherein at least one of the at least one rare earth disilicate layer or the at least one rare earth monosilicate layer includes an alkaline earth oxide dopant.
2. The environmental barrier coating system as claimed in claim 1, wherein the at least one rare earth disilicate layer is substantially hermetic.
3. The environmental barrier coating system as claimed in claim 1, wherein the at least one rare earth disilicate layer is doped and an amount of the alkaline earth oxide dopant is about 1-25 mole % of the layer.
4. The environmental barrier coating system as claimed in claim 3, wherein the amount of the dopant is about 10 mole % of the layer.
5. The environmental barrier coating system as claimed in claim 3, wherein the amount of the dopant increases the coefficient of thermal expansion of the at least one rare earth disilicate layer by no more than about 25%.
6. The environmental barrier coating system as claimed in claim 5, wherein the amount of the dopant increases the coefficient of thermal expansion of the at least one rare earth disilicate layer by less than about 10%.
7. The environmental barrier coating system as claimed in claim 3, wherein the alkaline earth oxide dopant comprises CaO and the at least one rare earth disilicate
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layer contains Y2O3.
8. The environmental barrier coating system as claimed in claim 7, wherein the at least one rare earth disilicate layer has a composition bounded by a region in the rare earth oxide/silica/alkaline earth oxide compositional space defined by a first composition point at Ca2Y8Si6O26, a second composition point at Y2SiO5, and a third composition point at Y2Si2O7.
9. The environmental barrier coating system as claimed in claim 7, wherein the at least one rare earth disilicate layer has a composition bounded by a region in the rare earth oxide/silica/alkaline earth oxide compositional space defined by a first composition point at Ca2Y8Si6O26, a second composition point at Ca3Y2Si6O18, and a third composition point at Y2Si2O7.
10. The environmental barrier coating system as claimed in claim 1, wherein the at least one rare earth monosilicate layer is doped and an amount of the alkaline earth oxide dopant is about 1-25 mole % of the layer.
11. The environmental barrier coating system as claimed in claim 10, wherein the amount of the dopant is about 10 mole % of the layer.
12. The environmental barrier coating system as claimed in claim 10, wherein the amount of the dopant increases the coefficient of thermal expansion of the at least one rare earth monosilicate layer by no more than about 10%.
13. The environmental barrier coating system as claimed in claim 10, wherein the alkaline earth oxide dopant comprises CaO and the at least one rare earth monosilicate layer contains Y2O3.
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14. The environmental barrier coating system as claimed in claim 13, wherein the at least one rare earth monosilicate layer has a composition bounded by a region in the rare earth oxide/silica/alkaline earth oxide compositional space defined by a first composition point at Y2O3, a second composition point at Ca2Y8Si6O26, and a third composition point at Y2SiO5.
15. The environmental barrier coating system as claimed in claim 1, wherein the amount of the dopant either reduces the coefficient of thermal expansion of the at least one rare earth disilicate layer or increases the coefficient of thermal expansion of the at least one rare earth monosilicate layer by less than about 10%.
16. The environmental barrier coating system as claimed in to claim 1, wherein at least one of the at least one rare earth disilicate layer or the at least one rare earth monosilicate layer further includes an alkaline-earth-rare-earth-silicate dopant of the formula AE•RE•S, where AE is Be, Mg, Ca, Sr, Ba, Ra, or combinations thereof, and RE is Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, or combinations thereof, and S is a compound containing an anionic silicon compound.
17. The environmental barrier coating system as claimed in claim 16, wherein the alkaline-earth-rare-earth-silicate dopant is a magnesium-rare-earth-silicate dopant.
18. The environmental barrier coating system as claimed in claim 16, wherein the alkaline-earth-rare-earth-silicate dopant is a calcium-rare-earth-silicate dopant.
19. The environmental barrier coating system as claimed in claim 18, wherein the calcium-rare-earth silicate dopant is CaYS.
20. The environmental barrier coating system as claimed in claim 19, wherein the layer including the alkaline-earth-rare-earth-silicate dopant has a composition
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including a composition point at Ca2Y2Si2O9 in the rare earth oxide/silica/alkaline earth oxide compositional space.
21. The environmental barrier coating system as claimed in claim 19, wherein the layer including the alkaline-earth-rare-earth-silicate dopant has a composition including a composition point at Ca3Y2Si3O12 in the rare earth oxide/silica/alkaline earth oxide compositional space.
22. The environmental barrier coating system as claimed in claim 19, wherein the layer including the alkaline-earth-rare-earth-silicate dopant has a composition including a composition point at Ca3Y2Si6O18 in the rare earth oxide/silica/alkaline earth oxide compositional space.
23. The environmental barrier coating system as claimed in claim 1, wherein the alkaline earth oxide dopant is CaO.
24. The environmental barrier coating system as claimed in claim 23, wherein the amount of the CaO dopant is about 1-25 mole % of the layer.
25. The environmental barrier coating system as claimed in claim 24, wherein the amount is about 2-20 mole % of the layer.
26. The environmental barrier coating system as claimed in claim 25, wherein the amount is about 2-10 mole % of the layer.
27. The environmental barrier coating system as claimed in claim 26, wherein the amount is about 10 mole % of the layer.
28. The environmental barrier coating system as claimed in claim 1, wherein the
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alkaline earth oxide dopant is MgO.
29. The environmental barrier coating system as claimed in claim 1, wherein the alkaline earth oxide dopant is SrO.
30. The environmental barrier coating system as claimed in claim 1, wherein the at least one rare earth disilicate layer is a composition of the formula RE2Si2O7, where RE is Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, or combinations thereof.
31. The environmental barrier coating system as claimed in claim 1, wherein the at least one rare earth monosilicate layer is a composition of the formula RE2SiO5, where RE is Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, or combinations thereof.
32. The environmental barrier coating system as claimed in claim 1, wherein both the at least rare earth monosilicate layer and the at least one rare earth disilicate layer include an alkaline earth oxide dopant.
33. The environmental barrier coating system as claimed in claim 1, wherein the at least one rare earth disilicate layer comprises two rare earth disilicate layers, and at least one of the two rare earth disilicate layers includes an alkaline earth oxide dopant.
34. A component of a gas turbine engine, wherein the component is coated with the environmental barrier coating system as claimed in claim 1.
35. The component as claimed in claim 34, wherein the component is formed of a ceramic matrix composite.
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36. The component as claimed in claim 35, wherein the environmental barrier coating system further comprises a bond coat that is between about 10 to about 200 µm thick.
37. The component as claimed in claim 36, wherein the at least one rare earth monosilicate layer is between about 10 to about 100 µm thick.
38. The component as claimed in claim 37, wherein the at least one rare earth disilicate layer is between about 10 to about 250 µm thick.
39. A gas turbine engine including the component as claimed in claim 34.
Dated this the 9th day of August, 2016
SANDEEP RAO
Agent for the Applicant [IN/PA -2098]
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