Removing Turbine Component Coatings Without Damage

摘要

Superalloy components require coating systems to protect base metals from the extraordinary operating environments of gas turbines. These tenacious coatings are designed to resist the oxidation and corrosion created by the combustion process in the turbine hot gas path. But these coatings also resist removal when they become depleted during operation. Most modern hot gas path coatings consist of a ceramic thermal barrier coating (TBC) on the outer surface and a "bond" coat between this TBC and the base metal. Typically, acid stripping and grit blasting of these bond coatings from superalloy components can cause both metallurgical and dimensional damage. Acid stripping and grit blasting of molybdenum, chrome, aluminum and yitterbium (MCrAlY) bond coatings from vanes, blades, shrouds, liners and transition pieces are destructive processes. Exposure to acid can result in stress corrosion cracking, pitting and alloy depletion. Grit blasting can result in uneven material removal and thinning of the base metal. Then there are the environmental issues that are becoming increasingly important.