Fabrication and cooling characteristics of microholes in nickel-based superalloys by femtosecond laser with large parameter-operating window

Turbine blades in aircraft engines operate under extreme high temperatures, with inlet temperatures reaching up to 2200 K. To reduce the blade temperature and extend service life, film cooling holes are typically designed. However, traditional micro-drilling techniques struggle to meet the high precision demands of modern aircraft engines. Femtosecond laser has emerged as an ideal method for processing film cooling holes due to its ultra-high precision and minimal heat-affected zone. However, the stringent requirements for processing film cooling holes on nickel-based alloys using femtosecond lasers result in a narrow selection range of laser parameters. Furthermore, researching the cooling characteristics of film cooling holes processed by lasers is also crucial in practical applications. In this study, the effects of laser parameters on the taper angle and surface morphology of micro-holes in nickel-based superalloys are investigated. Based on the actual morphology of micro-holes (serves as a film cooling hole) prepared by femtosecond laser, the effects of hole inclination and taper angle on their cooling characteristics are further investigated. The results show that both the surface morphology and taper angle can be effectively controlled by optimizing the process parameters. In micro-holes with well-defined inlet and outlet morphologies, the taper angle ranges from 4° to 8°. The cooling efficiency of air film holes with taper angles from 4° to 8° is similar, with cooling efficiency at the hole exit reaching up to 98 % and covering the parameters of our actual fabricating. This finding suggests that the process window of femtosecond laser fabricating of air film cooling holes is broadened, offering greater flexibility in selecting laser processing parameters.