Fluoride ion cleaning of gas turbine components using PTFE grease

An improved method for fluoride ion cleaning (FIC) utilizing the thermal decomposition of polytetrafluoroethylene (PTFE) powder was developed and applied to oxide scales on narrow deep cracks formed on the surface of gas turbine blades during service exposure. This method is characterized by directly filling-up the cracks with PTFE grease. The results of this improved method were compared with the conventional method. When processed in an FIC reactor using PTFE powder, the surface oxides in the cracks filled with PTFE grease were much better reduced and cleaned than those of unfilled. The difference was more evident at the deep and narrow crack tips, and was well attributed to the wetting and the subsequent capillary action of melted PTFE on the oxide surface in the cracks during the process.