Influence of heat accumulation during laser micromachining of CoCrMo alloy with ultrashort pulses in burst mode

This study presents experimental and theoretical results of material removal of cobalt chrome alloy (CoCrMo) using high-frequency picosecond laser pulses. Depending on the fluence and number of pulses in a burst, structures are created to be able to determine the ablated volume per pulse in burst, the structure depth and the surface roughness. A single pulse in the burst represents the ordinary pulsed laser radiation. Depending on the number of pulses, the ablated volume per pulse and the achieved depth of the structure, respectively, rises in the burst. Furthermore, a smoothing effect on the machined surface is revealed depending on selected parameters. An energy-dispersive X-ray analysis demonstrates that the stoichiometry remains the same after material processing in burst mode. To be able to simulate the material removal as well as the accumulated residual heat, the required parameters such as threshold fluence, effective penetration depth and the incubation factor are determined experimentally. The simulations demonstrate that laser-induced heat accumulation contributes to material removal and establish the smoothing effect through the use of the burst mode.