Shaping of zirconia by laser radiation for blow-out facilities of cooling holes in turbine blades

Turbine blades are provided with cooling holes in order to protect them against the heat of the burning process. To avoid hot spots on the cooled blade surface aerodynamic blow-out facilities are shaped into the thermal barrier coating (zirconia) by laser radiation of different pulse duration and wavelength. Drilling of cooling holes in a multilayer system (CMSX-4, MCrAlY, zirconia) of turbine blades is done by melt extraction with microsecond pulsed laser radiation (Nd:YAG slab laser, 1064nm, 350µs). The blow-out facilities (600x400µm2) are shaped by meandering scanning strategy using Nd:YAG laser radiation (1064nm, 40ps) that is focused on the zirconia surface or by mask-projection with excimer laser radiation (193nm, 25ns). The removal and surface roughness of zirconia are investigated as a function of laser power and overlap by white light interference microscopy (WIM). Crack formation in dependence on pulse duration and debris formation around the structured area are investigated by SEM and WIM. The scanning and the mask-projection strategy are compared concerning accuracy and flexibility of structuring.