Numerical and experimental investigations on 342 nm femtosecond laser ablation of K24 superalloy

Abstract

With the feature of ultrashort pulse width and ultrahigh peak power, femtosecond laser can realize real sense of ‘cold’ machining and it has been widely applied in micro and nano scale manufacturing. K24 is a new cast Ni-based superalloy with high strength, strong resistance to corrosion and excellent heat stability under high temperature. Micro drilling method of this kind of material has becomes a tough issue so far. In this paper, interaction process between 342nm femtosecond laser and K24 superalloy is theoretically described. Laser-dependent absorption coefficient and reflectivity of K24 superalloy are derived applying Planck equations while other physical properties like lattice heat capacity and electronic specific heat coefficient are calculated correlated with solid state physics utilizing linear superposition approximation. Based on these, finite difference method is employed to solve one-dimensional two-temperature model. Through corresponding verification experiments the accuracy of mathematical model is proved. The influence rules of machining parameters of 342nm femtosecond laser beam drilling, such as the feed distance of laser spot, scanning times, scanning velocity and laser average power, on the morphology of micro holes are deeply investigated through orthogonal experiments. Following theoretical analysis provide solid foundations for the future application of femtosecond laser drilling on superalloy.