Ablation effects of femtosecond laser functionalization on steel surfaces

In this work, the topographical and chemical effects of femtosecond laser irradiation on industrial 100Cr6 steel surfaces are analyzed. The irradiated areas present cavities with conical spikes at their center and an outer ring zone with periodical structures called sub-wavelength ripples. The number of pulses drastically influences the morphology of both zones. Abbott–Firestone curves show that 1 μm depth cavities have the best load capacity and might increase the lubrication efficiency due to their homogeneous topographic profile. The elemental depth profile obtained by X-ray photoelectron spectroscopy reveals that the laser irradiation produces a chemical carbide shift and increases the iron oxide layer thickness by a factor of 1.7 compared to the native layer. Raman analysis reveals the presence of metallic oxide and carbon bands. The distribution of amorphous and crystalline carbon depends on the distribution of the laser intensity. The increase of the number of pulses leads to the amorphization of the irradiated zones, according to the melt-quenching phenomena. These novel results permit a better understanding of the ablation phenomena in steels.