DD6 single-crystal superalloy with thermal barrier coating in femtosecond laser percussion drilling

In recent years, single-crystal superalloy and thermal barrier coating (TBC) have attracted considerable attentions in femtosecond laser drilling. Surface morphology changes in DD6 single-crystal superalloy and TBC induced by incident laser pulses with a wide range of powers (2.28–11.18 W) at 50 kHz are studied. The ablation thresholds of DD6 single-crystal superalloy and TBC are calculated, and the ablation mechanisms of different femtosecond laser spot regions are discussed in details. Results show that the ablation threshold of DD6 single-crystal superalloy is 1.16 J/cm², which is close to that of TBC (0.998 J/cm²). The femtosecond laser spot regions in the DD6 single-crystal superalloy and TBC can be divided into four (ablation, melting, laser-induced, and irradiated regions) on the basis of the energy distribution of the Gaussian laser beam. However, the physics behind femtosecond laser on single-crystal superalloy is laser-induced periodic surface structures (LIPSS), where is laser-induced cracks (LIC) on TBC. The dominant mechanism differs in different regions. The reason for cracks on the TBC may be the combined action of thermal stress and mechanism stress under high fluence and high repetition rate femtosecond laser.