CMSX-4, Bondcoat and TBCCopyright: Fraunhofer ILT
Multilayer systems are applied in gas turbines to combine good mechanical properties with chemical and thermal stability. A bulk material, e.g. the Ni-base alloy CMSX-4, is covered with a bond coat, which also protects it from high-temperature corrosion and serves as bond between the structure and the thermal barrier coating. The latter protects the workpiece from high temperatures.
Laser Drilling is the only efficient method to drill multilayersystems. The thermal barrier coating, which is the topmost layer, usually protects the workpiece from damage by high temperatur environments but it also prevents the application of other non-mechanical drilling processes, like Electrical Discharge Machining or Electrochemical Machining. Laser Drilling is applied to create precicesly shaped holes in a workpiece's surface with high angles towards its normal direction. Such drill-holes are e.g. used as cooling channels.