Abrasive Water Jet Drilling of Ceramic Thermal Barrier Coatings

Ceramic thermal barrier coatings (TBCs) are used to provide thermal insulation for aero-engine components from high temperature gas streams. It is difficult to drill small holes in TBC-coated components using electro-discharge machining (EDM) due to non-conductivity of the TBCs. This paper proposed a novel combined process to drill small holes in TBC-coated components through removing coating layers by abrasive water jet machining (AWJM) followed by drilling metallic substrate using EDM process. The present study investigated the first stage of the proposed process, i.e. AWJM drilling of TBCs with relative low-pressure. The influences of standoff distance, abrasives concentration, jet pressure and drilling time on machining results were evaluated. The relative low pressure (2-3 MPa) jet results in a W shape at bottom of the machined hole in case of 90 degrees impact angle. The exposed substrate diameter of the machined hole is smaller than TBC top diameter of that. The results show that the AWJM with relative low-pressure is an efficient and economical approach to remove TBC coatings and expose metal substrate for subsequent EDM drilling.