Ablation Characteristics and Material Removal Mechanism of Invar 36 Alloy Under Femtosecond Laser Irradiation

To investigate the ablation characteristics and material removal mechanism of Invar 36 alloy under femtosecond laser irradiation, a coupled flow-solid simulation model of femtosecond laser processing is established based on multi-physical fields and multi-scale effects. The validity of the simulation model is verified by femtosecond laser processing experiments. The material removal mechanism is investigated based on the simulation results. It is found that the material removal in femtosecond laser processing of Invar 36 alloy includes effects of hot melt corrosion, liquid phase explosion and gasification evaporation. There exists competitive mechanism of the three effects under various conditions. The ablative plume and the splashing state of droplets during the processing are rigorously investigated. The melt on the processed surface splits to form the comb-like micro-nano structures. Laser-induced periodic surface structures (LIPSSs) with “thin top and thick bottom” are formed at the top of micro-nano structures by evaporation. Under the influence of recoiling pressure, the top of the melt continues to split and form splashing droplets. Under the action of multi-pulse accumulation, the violent droplet splashing, which is phase explosion leads to a large amount of removal of molten material. The achieved processing simulation and the obtained research results of material removal mechanism of Invar 36 alloy under femtosecond laser irradiation in this paper provide a theoretical basis for the subsequent high-quality femtosecond laser processing of Invar 36 alloy.