The laser drilling of multi-layer aerospace material systems

Due to continuing advances in jet engine efficiency, components are exposed to ever-increasing combustion and exhaust gas temperatures. Air plasma sprayed thermal barrier coatings (TBCs) protect jet engine components from direct exposure to the corrosive temperatures. The TBC is affixed to the superalloy substrate by an intermediate bond coat thus producing a multi-layer material system. A laser drilling technique has been developed, to generate cooling holes in multi-layer systems, for use in the aerospace industry. The cooling holes are required to conform to standards stipulated by the original engine manufacturer (OEM). A Nd:YAG laser was used to study the parameters affecting hole generation in superalloy materials. This paper reports on the investigation into the negative effects of percussion laser drilling on material interfaces, bond strength, and the negative effects on the individual microstructures such as remelt layers and microcracking.