On interaction between laser and Ti6Al4V titanium alloy

Ultra-short Pulse Laser (USPL) has a wide range of applications in industrial sections. Among them is the workpiece surface pre-structuring before machining to reduce the process forces and temperature. Laser pre-structuring removes a section of workpiece material and induces controlled subsurface damages, improving the achievable Material Removal Rate (MRR) and workpiece machinability. USPL pre-structuring is used in various studies to optimize the conventional machining of titanium alloys. However, there is a lack of understanding of the interaction between USPL and titanium alloys associated with the laser scanning process concerning surface morphology, material removal mechanisms and geometrical features. The present work analyses the interactions between USPL and a titanium alloy as a difficult-to-cut material. A picosecond (p(s)) laser with a pulse duration of 12 p(s) was used for material ablation of titanium samples at different average laser powers P-L_ave, laser scan velocities v(L), and number of pulses N-p. The experimental studies were conducted in three categories of multiple pulses, single linear laser scanning and multiple linear laser scanning. For multiple pulses, the influence of pulse energy Ep on material ablation, changing surface morphology and melting formation was highlighted in a more significant role than the number of pulses. At E-p > 62.5 mu J, a substantial volume of melted material at the different number of pulses could be seen. In the case of linear laser scanning, laser input energy E-L_input was introduced as a parameter that includes the influence of successive pulses. In the single linear laser scanning, at laser input energy E-L_input greater than 125 J/cm(2), a tremendous rise in ablation depth was observed that corresponds to the huge melt formation on the surface of the lasered profile. At E-L_input < 125 J/cm(2), Laser-Induced Periodic Surface Structures (LIPSS) were observed and most of the lasered profile indicates considerably less or even no melting. In multiple linear laser scanning, lower scan velocities and average laser powers at constant E-L_input = 3.9 J/cm(2) led to more surface degradation, a more significant rise in ablation depth with the number of laser scanning Ns, deeper ablation depth, narrower lasered profile, less specific energy and MRR.