Thermal damage behavior and material removal mechanism during femtosecond and nanosecond laser ablation of refractory metal molybdenum

Abstract

This study focused on contrasting the thermal damage and material removal mechanisms of the refractory metal molybdenum in ablation processes generated by short-pulse lasers(nanosecond) and ultra-short-pulse(femtosecond) lasers. The laser-ablated zones of Mo with different pulse widths show different typical micro-morphologies. The femtosecond laser-ablated zone exhibits a higher depth-to-diameter ratio of 21.8:1 and features morphologies such as splash accumulation areas, laser-induced periodic surface structures (LIPSSs), and nanoparticle clusters. In contrast, the nanosecond laser-ablated zones display shallow pits, molten layers, pores, and cracks. The femtosecond laser causes less thermal damage to the microstructure and properties of refractory metal molybdenum. The femtosecond laser-ablated zone of refractory metal Mo has multiple recast layers with the thickness of 0.5–1.5 μm. There are fusion zones (FZs) of 3–4 μm deep and longitudinal cracks induced by residual stress on the surface of nanosecond laser-ablated zone. The splashed particles have a splash angle of 69.5° and they are mainly spherical particles of 200–500 nm in the femtosecond laser ablation process, during which the material is mainly removed by direct gasification. In the nanosecond laser ablation process, the splash angle of splashed particles is 85.2°, which are mainly spherical particles of 1–5 μm, and the material is mainly removed by liquid explosion. The influence of the laser pulse width on the laser ablation process of refractory metal Mo was quantitatively analyzed, thus forming a set of methodology systems for analyzing laser ablation characteristics of metals.

Keywords

• Molybdenum
• Laser ablation
• Pulse width
• Damage behaviors
• Removal mechanism