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A method for selectively removing oxide material from the surface of a substrate or coating disposed on the substrate is disclosed. The method includes the step of contacting the oxide material with an aqueous treatment composition having the formula HxAF6, wherein A can be Si, Ge, Ti, Zr, Al, and G

A method for selectively removing oxide material from the surface of a substrate or coating disposed on the substrate is disclosed. The method includes the step of contacting the oxide material with an aqueous treatment composition having the formula HxAF6, wherein A can be Si, Ge, Ti, Zr, Al, and Ga; and x is 1-6. The composition can sometimes include an additional acid, such as phosphoric acid, nitric acid, sulfuric acid, hydrochloric acid, hydrofluoric acid, and mixtures thereof. A method for replacing a worn or damaged protective coating applied over a substrate, utilizing the treatment composition, is also described.

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1. A method for removing at least one of: (1) an oxidized product of a substrate from a surface of the substrate, wherein the substrate is a turbine component formed of an alloy selected from the group consisting of a nickel based alloy, a cobalt based alloy, and an iron based alloy, or (2) an oxidi

1. A method for removing at least one of: (1) an oxidized product of a substrate from a surface of the substrate, wherein the substrate is a turbine component formed of an alloy selected from the group consisting of a nickel based alloy, a cobalt based alloy, and an iron based alloy, or (2) an oxidized product of a metallic coating disposed on the substrate from a surface of the metallic coating, wherein the substrate is the turbine component formed of the alloy, the method comprising the step of contacting the oxidized product of the substrate or the oxidized product of the metallic coating with an aqueous composition to remove a predetermined amount of the oxidized product of the substrate or a predetermined amount of the oxidized product of the metallic coating, wherein the aqueous composition consists essentially of an acid having the formula HxAF6 and water, wherein A is selected from the group consisting of Si, Ge, Ti, and Ga; and x is 1-6.2. The method of claim 1, wherein x is 1-3.3. The method of claim 1, wherein the acid is present at a level in the range of about 0.05 M to about 5 M.4. The method of claim 3, wherein the acid is present at a level in the range of about 0.2 M to about 3.5 M.5. The method of claim 1, wherein the aqueous composition is H2SiF6.6. A method for removing at least one of an oxidized product of a substrate from a surface of the substrate, wherein the substrate is a turbine component formed of an alloy selected from the group consisting of a nickel based alloy, a cobalt based alloy, and an iron based alloy an alloy comprising nickel, chromium, aluminum, or at least one of the foregoing metals, or a polymer, or an oxidized product of a metallic coating disposed on the substrate from a surface of the metallic coating, wherein the substrate is the turbine component formed of the alloy, the method comprising the step of contacting the oxidized product of the substrate or the oxidized product of the metallic coating with an aqueous composition to remove a predetermined amount of the oxidized product of the substrate or a predetermined amount of the oxidized product of the metallic coating, wherein the aqueous composition consists essentially of an acid having the formula HxAF6, at least one additional acid, and water, wherein A is selected from the group consisting of Si, Ge, Ti, and Ga; and x is 1-6.7. The method of claim 6, wherein the at least one additional acid has a pH of less than about 7 in water.8. The method of claim 7, wherein the at least one additional acid has a pH of less than about 3.5 in water.9. The method of claim 6, wherein the at least one additional acid is a mineral acid.10. The method of claim 6, wherein the at least one additional acid is selected from the group consisting of phosphoric acid, nitric acid, sulfuric acid, hydrochloric acid, hydrofluoric acid, hydrobromic acid, hydriodic acid, acetic acid, perchloric acid, phosphorous acid, phosphinic acid, alkyl sulfonic acids, and mixtures of any of the foregoing.11. The method of claim 6, wherein the at least one additional acid is phosphoric acid.12. The method of claim 6, wherein the at least one additional acid is present at a level less than about 80 mole %, based on the total moles of acid present in the aqueous composition.13. The method of claim 12, wherein the at least one additional acid is present at a level of about 20 mole % to about 70 mole %.14. The method of claim 1, wherein the oxide material is treated in a bath of the aqueous composition.15. The method of claim 14, wherein the bath is maintained at a temperature in the range of about room temperature to about 100° C., during treatment.16. The method of claim 15, wherein the temperature is in the range of about 45° C. to about 90° C.17. The method of claim 15, wherein the treatment time is in the range of about 10 minutes to about 72 hours.18. The method of claim 17, wherein the treatment time is in the range of about 60 minutes to about 20 hours.19. A method for removing at least one of: (1) an oxidized product of a substrate from a surface of the substrate, wherein the substrate is a turbine component formed of an alloy selected from the group consisting of a nickel based alloy, a cobalt based alloy, and an iron based alloy, or (2) an oxidized product of a metallic coating disposed on the substrate from a surface of the metallic coating, wherein the substrate is the turbine component formed of the alloy, the method comprising the step of exposing the oxidized product of the substrate or the oxidized product of the metallic coating to an aqueous composition to remove a predetermined amount of the oxidized product of the substrate or a predetermined amount of the oxidized product of the metallic coating, wherein the aqueous composition consists essentially of an acid having the formula HxAF6 and water, wherein A is selected from the group consisting of Si, Ge, Ti, and Ga; and x is 1-6, and wherein the precursors to said acid comprise any compound or group of compounds which can be combined to form the acid or its dianion AF6?2.20. A method for removing an oxide material from a diffusion- or overlay coating on the surface of a turbine engine component, comprising the step of contacting the oxide material with an aqueous composition to selectively remove the oxide material from the diffusion or the overlay coating, wherein the aqueous composition comprises H2SiF6, wherein the diffusion coating comprises an aluminide alloy, and wherein the overlay coating comprises a composition having a formula of MCrAl(X), wherein M is an element selected from the group consisting of Ni, Co, Fe, and combinations thereof, and wherein X is an element selected from the group consisting of Y, Ta, Si, Hf, Ti, Zr, B, C, and combinations thereof.21. The method of claim 20, wherein the aqueous composition further comprises an additional acid selected from the group consisting of phosphoric acid, nitric acid, sulfuric acid, hydrochloric acid, hydrofluoric acid, and mixtures thereof, wherein the additional acid is present at a level less than about 80 mole %, based on the total moles of acid present in the aqueous composition.22. The method of claim 20, wherein the oxide material is also initially present in at least one cavity within the turbine engine component, and is removed therefrom during treatment with the aqueous composition.23. A method for replacing a protective coating applied over a substrate, comprising the following steps:(i) removing an oxide material from a surface of the protective coating disposed on the substrate by contacting the oxide material with an aqueous composition which comprises an acid having the formula HxAF6, or precursors to said acid, wherein A is selected from the group consisting of Si, Ge, Ti, and Ga; and x is 1-6; (ii) removing the protective coating disposed on the substrate by contacting the protective coating with the aqueous composition; and (iii) applying a new protective coating to the substrate. 24. The method of claim 23, wherein steps (i) and (ii) are carried out simultaneously, using the same aqueous composition.25. The method of claim 24, wherein the aqueous composition further comprises at least one additional acid or precursor thereof.26. The method of claim 25, wherein the additional acid is selected from the group consisting of phosphoric acid, nitric acid, sulfuric acid, hydrochloric acid, hydrofluoric acid, hydrobromic acid, hydriodic acid, acetic acid, perchloric acid, phosphorous acid, phosphinic acid, alkyl sulfonic acids, and mixtures of any of the foregoing.27. The method of claim 23, wherein the coating removed in step (ii) and the coating applied in step (iii) are each selected from the group consisting of diffusion coatings and overlay coatings.28. The method of claim 23, wherein the new coating of step (iii) is applied by a technique selected from the group consisting of vacuum plasma spray (VPS); air plasma spray (APS); high velocity oxy-fuel (HVOF); sputtering; physical vapor deposition (PVD); electron beam physical vapor deposition (EB-PVD); and diffusion-aluminiding.