Drilling of cooling holes and shaping of blow-out facilities in turbine blades by laser radiation

Drilling of cooling holes (diameter 200µm) by melt expulsion with microsecond pulsed laser radiation in a multilayer system (Ni-superalloy CMSX-4, VPS-McrAlY, EB-PVD-zirconia) of turbine blades is reported. The quality of drilled holes, e.g. conicality determined by optical (OM) and electron (SEM) microscopy, heat affected zone (HAZ) and recast analyzed by SEM after metallographical preparation and chemical composition of the resolidified zone measured by EDX are presented for different processing gases (oxygen, argon and nitrogen). To avoid hot spots on the cooled blade surface shaping of aerodynamic blow-out facilities in the TBC (zirconia) is done by laser radiation of different pulse length and wavelength. Two different strategies to structure the zirconia are investigated: mask-projection and scanning. The average removal depth and average surface roughness determined by white light interference microscopy (WIM) are presented in dependence on average laser power and overlap of the laser pulses. The formation of cracks while shaping is analyzed by SEM.