Femtosecond laser micromachining of single-crystal superalloys

Investigations on femtosecond laser micromachining of single crystal superalloys with and without plasma-sprayed thermal barrier coatings were conducted under laser fluences ranging from 0.1 J/cm(2) up to 160 J/cm(2). Micromachining was carried out in air using a titanium: sapphire laser system (lambda = 780 nm) operating at a repetition rate of 1 kHz and delivering individual pulses of similar to 150 fs duration. The ablation threshold of the single crystal superalloy was determined as 203 +/- 20 mJ/cm(2). Laser-induced damage was examined by means of scanning electron microscopy and transmission electron microscopy. These studies indicate a complete absence of any melting, recast layers, heat-affected zones or microcracks in the vicinity of the machining area. The only form of damage observed in the single crystal superalloy machined near or above the ablation threshold was a laser-induced plastically deformed layer with a maximum extent of similar to 5 mu m. Machining through ceramic thermal barrier coatings on a superalloy produced no delamination along the superalloy/coating interfaces or cracks within the TBC or bond coat. The residual roughness of the machined surface was in the sub-micron range. The present study suggests that femtosecond laser micromachining is a very promising technique for production of fine-scale features in multi-layer material systems for aerospace and power generation components.