초록 ▼

A method for selectively removing an aluminide coating from at least one surface of a metal-based substrate by: (a) contacting the surface of the substrate with at least one stripping composition comprising nitric acid at a temperature less than about 20째 C. to degrade the coating without damaging t

A method for selectively removing an aluminide coating from at least one surface of a metal-based substrate by: (a) contacting the surface of the substrate with at least one stripping composition comprising nitric acid at a temperature less than about 20째 C. to degrade the coating without damaging the substrate; and (b) removing the degraded coating without damaging the substrate. Also disclosed is a method for replacing a worn or damaged aluminide coating on at least one surface of a metal-based substrate by selectively removing the coating using the above steps, and then applying a new aluminide coating to the surface of the substrate. Turbine engine parts, such as high-pressure turbine blades, treated using the above methods are also disclosed.

대표청구항 ▼

What is claimed is: 1. A method for selectively removing an aluminide coating from at least one surface of a metal-based substrate, comprising the following steps in sequence: (a) contacting the surface of the substrate with an aqueous solution comprising from about 10% to about 50%, by weight of t

What is claimed is: 1. A method for selectively removing an aluminide coating from at least one surface of a metal-based substrate, comprising the following steps in sequence: (a) contacting the surface of the substrate with an aqueous solution comprising from about 10% to about 50%, by weight of the solution, of caustic at a temperature of from about 60째 C. to about 100째 C. for from about 20 minutes to about 4 hours; (b) contacting the surface of the substrate with at least one stripping composition comprising from about 20% to about 40% nitric acid, by weight of the composition, at a temperature less than about 20째 C. for at least about 2 hours to degrade the coating without damaging the substrate; and (c) removing the degraded coating without damaging the substrate. 2. The method of claim 1, wherein the stripping composition comprises from about 25% to about 35% nitric acid, by weight of the composition. 3. The method of claim 2, wherein the stripping composition comprises from about 28% to about 32% nitric acid, by weight of the composition. 4. The method of claim 1, wherein the stripping composition has a temperature of from about 0째 C. to about 15째 C. 5. The method of claim 4, wherein the stripping composition has a temperature of from about 4째 C. to about 12째 C. 6. The method of claim 1, wherein the stripping composition contacts the substrate for a period of from about 4 hours to about 10 hours. 7. The method of claim 6, wherein the stripping composition contacts the substrate for a period of from about 6 hours to about 8 hours. 8. The method of claim 6, wherein the stripping composition comprises from about 25% to about 35% nitric acid, by weight of the composition, and has a temperature of from about 4째 C. to about 12째 C. 9. The method of claim 8, wherein the stripping composition further comprises from about 01. % to about 5%, by weight of the composition, of a wetting agent selected from the group consisting of polyalkylene glycols, glycerol, fatty acids, soaps, emulsifiers, and surfactants. 10. The method of claim 9, wherein the substrate is immersed in a bath of the stripping composition in step (b) for a period of from about 6 hours to about 8 hours. 11. The method of claim 1, wherein the stripping composition further comprises from about 0.1% to about 5%, by weight of the composition, of a wetting agent. 12. The method of claim 1, wherein the substrate is immersed in a bath of the stripping composition in step (b). 13. The method of claim 12, wherein the bath is maintained at a temperature of from about 0째 C. to about 15째 C. while the substrate is immersed therein for a period of from about 4 hours to about 10 hours. 14. A method for selectively removing an aluminide coating from at least one internal surface of a metal-based substrate, comprising the following steps in sequence: (a) contacting the surface of the substrate with an aqueous solution comprising from about 10% to about 50%, by weight of the solution, of caustic at a temperature of from about 60째 C. to about 100째 C. for from about 1 to about 4 hours; (b) contacting the surface of the substrate with at least one stripping composition comprising from about 20% to about 40% nitric acid, by weight of the composition, at a temperature less than about 20째 C. for at least about 2 hours to degrade the coating without damaging the substrate; (c) contacting the surface of the substrate with an aqueous solution comprising from about 10% to about 50%, by weight of the solution, of caustic at a temperature of from about 60째 C. to about 100째 C. for from about 20 minutes to about 2 hours; (d) contacting the surface of the substrate with at least one stripping composition comprising from about 20% to about 40% nitric acid, by weight of the composition, at a temperature less than about 20째 C. for at least about 2 hours to degrade the coating without damaging the substrate; and (e) contacting the surface of the substrate with an aqueous solution comprising from about 10% to about 50%, by weight of the solution, of caustic at a temperature of from about 60째 C. to about 100째 C. for from about 1 to about 4 hours to remove the degraded coating without damaging the substrate. 15. The method of claim 14, wherein the substrate is immersed in a bath of the stripping composition maintained at a temperature of from about 0째 C. to about 15째 C. in each of steps (b) and (d). 16. The method of claim 15, wherein the stripping composition comprises from about 25% to about 35%, by weight, of nitric acid. 17. The method of claim 16, wherein the substrate is immersed in the bath of the stripping composition having a temperature of from about 4째 C. to about 12째 C. for from about 3 to about 4 hours in each of steps (b) and (d). 18. The method of claim 17, wherein the substrate is immersed in a bath of the caustic solution having a temperature of from about 70째 C. to about 85째 C. in each of steps (a), (c) and (e). 19. The method of claim 18, wherein the caustic solution comprises from about 15% to about 30%, by weight, of potassium hydroxide. 20. The method of claim 19, wherein the caustic solution is ultrasonically agitated while in contact with the substrate. 21. The method of claim 20, wherein the aluminide coating is selectively removed from the internal surfaces of a high-pressure turbine blade. 22. A method for selectively removing an aluminide coating from at least one internal surface of a superalloy substrate, comprising the following steps in sequence: (a) contacting the surface of the substrate with an aqueous solution comprising from about 10% to about 50%, by weight of the solution, of caustic at a temperature of from about 60째 C. to about 100째 C. for from about 20 minutes to about 4 hours, (b) contacting the surface of the substrate with at least one stripping composition comprising from about 25% to about 35% nitric acid, by weight of the composition, at a temperature of from about 0째 C. to about 15째 C. for from about 4 hours to about 10 hours to degrade the coating without damaging the substrate; and (c) removing the degraded coating without damaging the substrate. 23. The method of claim 22, wherein the stripping composition comprises from about 28% to about 32% nitric acid, and the substrate is immersed in a bath of the stripping composition having a temperature of from about 4째 C. to about 12째 C. for from about 6 hours to about 8 hours. 24. A method for replacing a worn or damaged aluminide coating on at least one surface of a metal-based substrate, comprising the following steps in sequence: (i) selectively removing the aluminide coating from the surface of the substrate by (a) contacting the surface of the substrate with an aqueous solution comprising from about 10% to about 50%, by weight of the solution, of caustic at a temperature of from about 60째 C. to about 100째 C. for from about 20 minutes to about 4 hours; (b) contacting the surface of the substrate with at least one stripping composition comprising from about 20% to about 40% nitric acid, by weight of the composition, at a temperature of less than about 20째 C. for at least about 2 hours to degrade the coating without damaging the substrate; and (c) removing the degraded coating without damaging the substrate; and (ii) applying a new aluminide coating to the surface of the substrate. 25. The method of claim 24, wherein the stripping composition comprises from about 28% to about 32% nitric acid, and the substrate is immersed in a bath of the stripping composition having a temperature of from about 4째 C. to about 12째 C. for from about 6 hours to about 8 hours.