Investigation into femtosecond based laser ablation and morphology of micro-hole in titanium alloy

Abstract

Creating good surface quality micro holes for cooling gas turbine blades made of titanium alloy is still challenging for manufacturers of aerospace engine components. Therefore, the goal of this work is to comprehend how an ultra-short pulse laser interacts with titanium alloy and to explore the effect of laser fluence, pulse overlap and pulse repetition rate on hole diameter, depth, heat affected zone and recast layer. The threshold for femtosecond laser ablation is determined for different laser fluence, pulse repetition rates, and hole sizes. By using a 3D profilometer and field emission scanning electron microscopy, the ablated micro hole features are determined. Regardless of laser fluence or hole size, better micro hole shape is seen at a threshold repetition rate of 10 kHz. Better hole geometry is obtained at fluence of 0.44 J/cm2, 10 kHz repetition rate and 85% of pulse overlap. At higher pulse overlap, micro-cracks, heat-affected zones, and recast layers are more prominent, which is related to higher heat accumulation since titanium alloy has a low thermal conductivity.