Numerical simulation on nanosecond laser ablation of titanium considering plasma shield and evaporation-affected surface thermocapillary convection

Nanosecond laser ablation of metal is a complicated process, which consists of many strongly coupled physical phenomena, including material heating, melting, evaporation, vapour dynamics, and plasma shield. In this work, the nanosecond laser ablation process of titanium is investigated at 1064 nm wavelength. A multi-physics axisymmetric two-dimensional (2D) model is presented. The evolution and the distribution of titanium target's temperature were solved using governing equations and the vapour dynamics was determined using the Knudsen relations. The maximum temperature of titanium grown slower with the increase in laser fluence and the maximum flow velocity of liquid materials reached 121 m/s with the laser fluence of 12 J/cm². In addition, the plasma shield effect was taken into account to correct the energy distribution of the incident laser. As the laser fluence increases, the energy efficiency decreases. At the laser fluence of 12 J/cm only 55.9% of the energy was absorbed at the centre of titanium. Furthermore, the surface morphology profiles were analysed after the laser ablation on different laser fluences lying within the range of 2 - 12 J/cm². The results showed that the surface morphology after ablation has a crater-like form and the increment of laser fluence leads to a slower non-linear increment in ablation depth and diameter of melt zone. The calculated results are in good agreement with the experimental results. The study provides useful information for nanosecond laser precision fabrication.