Laser micromachining of metallic glasses. Investigation of the material response to machining with micro - second and pico - second lasers

Metallic glasses have been preferred to crystalline alloys for applications in microelectronics mechanical systems and die components because of their ease of formability and excellent mechanical properties. This paper presents the machining response of amorphous and polycrystalline Ni-based alloys (Ni-78 B-14 Si-8) and Fe alloys (Fe-81 B-13.5 Si-3.5 C-2) when subjected to micro-second and pico-second laser processing. The shape and topography of craters created with single pulses as a function of laser energy together with holes drilled and laser milled areas in both materials were studied. Focused ion beam (FIB) imaging and Energy Diffraction Spectroscopy (EDS) were used to analyse the single craters, through holes and milled trenches in the amorphous and polycrystalline samples. The material microstructure analysis revealed that processing both materials with micro-second and pico-second lasers does not lead to crystallisation and the short-range atomic ordering of metallic glasses can be retained. When processing the amorphous sample the material laser interactions resulted in a significant ejection of molten material from the bulk that was then followed by its partial re-deposition around the craters. Additionally, there were no signs of crack formation that indicate a higher surface integrity after laser machining. This integrity is closely related to the nature of the metallic glass. A conclusion is made that laser processing both with short-and long-pulses is a promising technique for micromachining metallic glasses because it does not lead to material crystallisation, preserving the good mechanical properties of these sort of materials.