Impact of the laser irradiation parameters on the surface characteristics of coarse- and ultra-fine-grained β-Ti alloy

Abstract

The purpose of this study was to investigate the effect of laser irradiation in different gas atmospheres on the surface properties of coarse-grained (CG) and ultra-fine- grained (UFG) β-Ti alloys with emphasis on surface roughness, chemistry and ablation. Field-emission scanning electron microscopy was used to obtain information on the surface morphology of the irradiated area, energy dispersive spectroscopy was utilized to analyze the chemical composition in the central irradiated area, while profilometric analysis was conducted to attain information on the surface topography of the irradiated area. Laser-generated surface structures in the form of conically- shaped craters, ripples, and droplets, as well as periodic and capillary waves on the morphologically and chemically altered CG and UFG alloy surface, were developed as a result of the hydrodynamic and oxidation processes occurring during the laser beam and alloy interaction. Also, during the process of laser surface modification, the laser- induced plasma was created in front of the irradiated alloy surface. Results attained during the present study showed that the alloy surface properties were noticeably impacted by the alterations of laser irradiation intensity and applied gas atmosphere. Namely, under the ultra-short pulsed irradiation conditions the presence of more pronounced surface structures, increased damage degree along the target depth, appearance of more distinct ejected, melted, and solidified material, as well as noticeable material evaporation were evident over the whole irradiated area. Moreover, the application of higher laser output energy led to an increase in the surface damage features dimensions, and an enhancement of the surface roughness and volume of the ablated material which, in turn, caused more intensive surface oxidation. Finally, the conducted research showed that the presence of refined UFG microstructure significantly contributed to the enhanced impact of the laser irradiation process on the occurrence of surface alterations that are favorable for the applicability of the investigated β-Ti alloy in orthopedic and dental implantology.