UV N2 laser ablation of a Cu–Sn–Zn–Pb alloy: Microstructure and topography studied by focused ion beam

A Cu–Sn–Zn–Pb alloy was irradiated by ultraviolet nitrogen laser pulses (N2 laser, wavelength 337 nm, pulse duration 6 ns, frequency 1 Hz, power 0.5 MW and average power density 0.67 GW/m2). The surface topography and microstructure were mainly studied by scanning electron microscopy, and a focused ion beam. The non-homogenized spatial beam profile resulted in the activation of several ablative mechanisms, the main being phase explosion and hydrodynamic instability. They caused a crater to be formed, surrounded by a raised rim and wavelike structure in a halo. FIB cross-sectioning and imaging showed a shallow (few micrometers) molten and resolidified surface layer. Streaks were observed in the heat-affected zone beneath the molten layer, indicating partial recrystallization of initially cold-worked material.