Cladding, drilling, and shaping of aerospace and power plant components by laser radiation
Drilling of cooling holes (diameter about 200µm) in a multilayer system (CMSX-4, MCrAlY, zirconia) of turbine blades enabling effusion cooling is performed via melt extraction by pulsed laser radiation (Nd:YAG slab, 1064nm, 100-500µs). Aerodynamical hole outlets (600x400µm2) are shaped by meandering scanning strategy using pulsed laser radiation (Nd:YAG-DL regenerative amplifier, 1064nm, 80ps) 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. Cladding on turbine components by CO2 and Nd:YAG laser radiation is carried out using powder additive materials of the same sort (e. g. titanium-based alloys: Ti Al6 V4, Ti 6242, Ti 6246 etc. and nickel-based high temperature alloys: In 625, In 718, In 738 etc.) Processing basics and specifications like single-stage processing, powder feeding, gas shielding etc. are described. The dependencies of microstructure, epitaxy, micro-porosity, metallurgical bond defects, mixing, geometry of HAZ, geometrical accuracy and roughness on processing variables like laser power, scanning speed, powder mass flow and gas shielding flow etc. are discussed on selected clads and materials. Applications like repair of blade tips and seals (e. g. Ti Al6 V4, In 718) as well as manufacturing of whole blades are presented. Results are characterized by optical microscopy and hardness testing.