Strain tolerant corrosion protecting coating and spray method of application

Abstract

A corrosion resistant coating for gas turbine engine includes a glassy ceramic matrix wherein the glassy matrix is silica-based, and includes corrosion resistant particles selected from refractory particles and non-refractory MCrAlX particles, and combinations thereof. The corrosion resistant particles are substantially uniformly distributed within the matrix, and provide the coating with corrosion resistance. Importantly the coating of the present invention has a coefficient of thermal expansion (CTE) greater than that of alumina at engine operating temperatures. The CTE of the coating is sufficiently close to the substrate material such that the coating does not spall after frequent engine cycling at temperatures above 1200° F.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a portion of the turbine section of a gas turbine engine.

FIG. 2 is a cross-sectional view of a superalloy substrate having a surface coated with the coating of the present invention.

FIG. 3 is a perspective view of a turbine disk, as viewed from the front or fan portion of the engine in the direction of gas flow, showing where the corrosion resistant coating of this invention can be desirably located.

FIG. 4 depicts a superalloy (RENE® 88DT) coupon coated with the first embodiment coating composition of the present invention before cyclic thermal adhesion (FCT) and corrosion testing.

FIG. 5 is a photomicrograph of the coupon of FIG. 5 after cyclic thermal adhesion testing (FCT).

FIG. 6 depicts an exemplary superalloy (RENE® 88DT) coupon coated with the first embodiment of the present invention, shown after corrosion testing.

FIG. 7 depicts comparative results of superalloy (RENE® 88DT) coupons coated with the first embodiment of the coating composition versus coupons coated with the SermaFlow® 3000 after cyclic thermal adhesion (FCT) testing.

FIG. 8 further graphically depicts the results of low cycle fatigue testing of superalloy (RENE® 88DT) coupons coated with the first embodiment of the coating composition of the present invention.

FIGS. 9 a-9c depict comparative results of FCT testing of an exemplary coating composition of the first embodiment of the present invention versus an exemplary the coating composition of the second embodiment of the present invention, wherein the CTE of the second composition is selected to closely match that of the superalloy substrate, and wherein two coating thicknesses were provided in the second embodiment.

FIGS. 10 a and 10b depict cross-sectional photomicrograph views of the coupon of FIG. 9b, showing particle size distribution and coating thickness of the corrosion resistant particulates.

FIGS. 11 a and 11b depict cross-sectional photomicrograph views of the coupon of FIG. 9c, showing particle size distribution and coating thickness of the corrosion resistant particulates.

Claims

1. A corrosion resistant coating composition comprising: a binder free of hexavalent chromium, the binder comprising silicone, the binder comprising from about 5 to about 45 weight percent of the coating composition;a corrosion resistant particulate, the corrosion resistant particulate comprising a refractory particulate having a coefficient of thermal expansion greater than or equal to that of alumina as determined at a temperature of 1200° F., the corrosion resistant particulate comprising about 15 to about 92 percent by weight of the composition; anda non-aqueous solvent, the solvent comprising from about 3 to about 50 percent by weight of the composition.

2. The coating composition of claim 1, wherein the refractory particulate is selected from the group consisting of alumina, zironcia, hafnia, yttria stabilized zirconia, yttria stabilized hafnia, ceria, chromia, magnesia, iron oxide, titania, yttria, and yttrium aluminum garnet, and combinations thereof.

3. The coating composition of claim 2, wherein the silicone binder comprises a siloxane.

4. The coating composition of claim 1, wherein the corrosion resistant particulate further comprises a non-refractory particulate selected from the group consisting of MCr, MCrX, MAl, MAlX or MCrAlX, where M is an element selected from nickel, iron cobalt and combinations thereof and X is an element selected from the group consisting of Ta, Re, Y, Zr, Hf, La, Si, B, C and combinations thereof, and wherein the non-refractory particulate has a coefficient of thermal expansion that is greater than that of alumina as determined at a temperature of 1200° F.

5. The coating composition of claim 4, wherein the coating composition comprises from about 5 to about 45 weight percent binder, from about 3 to about 50 weight percent solvent, from about 10 to about 87 weight percent non-refractory particles, and from about 5 to about 82 weight percent refractory particles.

6. The coating composition of claim 5, wherein the corrosion resistant particulate comprises between about 5 to about 10 weight percent cobalt, about 25 to about 40 weight percent nickel, about 15 to about 25 weight percent chromium, about 5 to about 15 weight percent aluminum, and about 0.10 to about 1.5 weight percent yttrium.

7. The coating composition of claim 5, wherein the corrosion resistant particulate comprises between about 50 to about 75 weight percent nickel, about 15 to about 25 weight percent chromium, about 5 to about 15 weight percent aluminum, and about 0.10 to about 1.5 weight percent yttrium.

8. The coating composition of claim 5, wherein the corrosion resistant particulate comprises between about 85 to about 95 weight percent iron, and between about 5 to about 15 weight percent aluminum.

9. A coated article comprised of a superalloy substrate and corrosion resistant coating, the article comprising: a superalloy substrate; anda coating composition applied to the superalloy substrate, the coating composition comprising, before curing and firing: a binder free of hexavalent chromium, the binder comprising silicone, the binder comprising from about 5 to about 45 weight percent of the composition;a corrosion resistant particulate, the corrosion resistant particulate comprising a refractory particulate having a coefficient of thermal expansion greater than or equal to that of alumina as determined at a temperature of 1200° F., the corrosion resistant particulate comprising about 15 to about 92 percent by weight of the composition; anda non-aqueous solvent, the solvent comprising from about 3 to about 50 percent by weight of the composition.

10. The coated article of claim 9, wherein the corrosion resistant particulate comprises alumina, zironcia, hafnia, yttria stabilized zirconia, yttria stabilized hafnia, ceria, chromia, magnesia, iron oxide, titania, yttria, and yttrium aluminum garnet, and combinations thereof.

11. The coated article of claim 10, wherein the corrosion resistant particulate further comprises a non-refractory particulate selected from the group consisting of MCr, MCrX, MAl, MAlX or MCrAlX, where M is an element selected from nickel, iron, cobalt and combinations thereof and X is an element selected from the group consisting of Ta, Re, Y, Zr, Hf, La, Si, B, C and combinations thereof, and wherein the non-refractory particulate has a coefficient of thermal expansion that is greater than that of alumina as determined at a temperature of 1200° F.

12. The coated article of claim 11, wherein the coating composition comprises from about 5 to about 45 weight percent binder, from about 3 to about 50 weight percent solvent, from about 10 to about 87 weight percent non-refractory particles, and from about 5 to about 82 weight percent refractory particles.

13. The coated article of claim 12, wherein the corrosion resistant particulate comprises between about 5 to about 10 weight percent cobalt, about 25 to about 40 weight percent nickel, about 15 to about 25 weight percent chromium, about 5 to about 15 weight percent aluminum, and about 0.10 to about 1.5 weight percent yttrium.

14. The coated article of claim 12, wherein the corrosion resistant particulate comprises between about 50 to about 75 weight percent nickel, about 15 to about 25 weight percent chromium, about 5 to about 15 weight percent aluminum, and about 0.10 to about 1.5 weight percent yttrium.

15. The coated article of claim 12, wherein the corrosion resistant particulate comprises between about 85 to about 95 weight percent iron, and between about 5 to about 15 weight percent aluminum.

16. A coated article comprised of a superalloy substrate and corrosion resistant coating, the article comprising: a superalloy substrate having an outer surface, the outer surface having a first corrosion resistant coating thereon; anda coating composition overlying the first corrosion resistant coating, the coating composition comprising, before curing and firing: a binder free of hexavalent chromium, the binder comprising silicone, the binder comprising from about 5 to about 45 weight percent of the composition;a corrosion resistant particulate, the corrosion resistant particulate comprising a refractory particulate having a coefficient of thermal expansion greater than or equal to that of alumina as determined at a temperature of 1200° F., the corrosion resistant particulate comprising about 15 to about 92 percent by weight of the composition; anda non-aqueous solvent, the solvent comprising from about 3 to about 50 percent by weight of the composition.

17. The coated article of claim 16, wherein the first corrosion resistant coating is selected from the group consisting of MCrAlX coatings, aluminides, and noble metal-modified aluminides.

18. A method of coating a superalloy substrate with a corrosion resistant coating composition, the method comprising the steps of: providing a superalloy substrate having a surface to be coated;treating the surface of the superalloy substrate to enhance its adhesion characteristics;providing a sprayable coating composition, the composition comprising: a binder free of hexavalent chromium, the binder comprising silicone, the binder comprising from about 5 to about 45 weight percent of the composition;a corrosion resistant particulate, the corrosion resistant particulate comprising a refractory particulate having a coefficient of thermal expansion greater than or equal to that of alumina as determined at a temperature of 1200° F., the corrosion resistant particulate comprising about 15 to about 92 percent by weight of the composition; anda non-aqueous solvent, the solvent comprising from about 3 to about 50 percent by weight of the composition;spraying the coating composition onto at least a portion of the surface of the superalloy substrate;drying the composition to remove unbound fluid from the slurry and to form a coating of preselected thickness on at least a portion of the surface of the component; andfiring the coating to form at least a glassy matrix having substantially uniformly distributed corrosion resistant particles.

19. The method of claim 18, wherein the corrosion resistant particulate further comprises a non-refractory particulate selected from the group consisting of MCr, MCrX, MAl, MAlX or MCrAlX, where M is an element selected from nickel, iron, cobalt and combinations thereof and X is an element selected from the group consisting of Ta, Re, Y, Zr, Hf, La, Si, B, C and combinations thereof, and wherein the non-refractory particulate has a coefficient of thermal expansion that is greater than that of alumina as determined at a temperature of 1200° F.

20. The method of claim 18, wherein the step of firing the coating is performed at a temperature that is less than or equal to the operating temperature that the substrate surface is expected to experience in operation.

21. A coated article comprised of a superalloy substrate and corrosion resistant coating, the article comprising: a superalloy substrate; anda coating applied to the superalloy substrate, the coating comprising: a binder free of hexavalent chromium, the binder comprising silicone, the binder comprising from about 5 to about 75 weight percent of the coating; anda corrosion resistant particulate, the corrosion resistant particulate comprising a refractory particulate having a coefficient of thermal expansion greater than or equal to that of alumina as determined at a temperature of 1200° F., the corrosion resistant particulate comprising about 25 to about 95 percent by weight of the coating.

22. The coated article of claim 21, wherein the binder forms a glass matrix upon heating to a first preselected temperature and wherein the corrosion resistant particles are substantially uniformly distributed in the matrix.

23. The coated article of claim 22, wherein the binder forms a glassy ceramic matrix upon heating to a second preselected temperature, the second preselected temperature being greater than the first preselected temperature.

24. A coated article comprised of a superalloy substrate and corrosion resistant coating, the article comprising: a superalloy substrate having an outer surface, the outer surface having a first corrosion resistant coating thereon; anda second coating overlying the first corrosion resistant coating, the second coating comprising: a binder free of hexavalent chromium, the binder comprising silicone, the binder comprising from about 5 to about 75 weight percent of the second coating; anda corrosion resistant particulate, the corrosion resistant particulate comprising a refractory particulate having a coefficient of thermal expansion greater than or equal to that of alumina as determined at a temperature of 1200° F., the corrosion resistant particulate comprising about 25 to about 95 percent by weight of the second coating.

25. The coated article of claim 24, wherein the binder forms a glass matrix upon heating to a first preselected temperature and wherein the corrosion resistant particles are, substantially uniformly distributed in the matrix.

26. The coated article of claim 25, wherein the binder forms a glassy ceramic matrix upon heating to a second preselected temperature, the second preselected temperature being greater than the first preselected temperature.