Molten metal hydroxide removal of thermal barrier coatings

During both the manufacture of new engine components and the refurbishment of engine run airfoils, it is often necessary to strip a thermal barrier coating (TBC). Ceramic coatings deposited by electron beam physical vapor deposition (EB-PVD) can be removed by grit blasting, reaction with halide gas, autoclave, or high-pressure water jet processes. However, these techniques are expensive, labor intensive, time consuming and process control is typically poor. In addition, prior art TBC strip processes often cause damage to the bond coat and/or substrate. A research program was undertaken to determine whether immersion of ceramic coated components in molten potassium hydroxide at atmospheric pressure can remove a TBC in a short time without damaging either the bond coat or the substrate. This method of removing ceramic coatings is described and the effects of the process on a variety of superalloys, bond coats, and zirconia coating combinations are presented and discussed.