Effect of Laser treatment on the microstructure and mechanical properties of the surface of Ti-6Al-4V alloy fabricated by Powder Bed Fusion technology

This study investigates the influence of laser surface treatment under different protective atmospheres (air, argon, and nitrogen) on the microstructure, mechanical, tribological, and biological properties of Ti-6Al-4V alloy produced by selective laser melting (SLM). A continuous-wave laser (200 W, 1070 nm) was used to remelt the surfaces of as-printed samples. Comprehensive characterization was performed using XRD, XPS, Raman spectroscopy, SEM/EDS, hardness testing, tribological measurements, and in-vitro cytotoxicity assays. The laser-treated samples exhibited a significant transformation of the surface microstructure from martensitic α′-Ti to a fine α + β phase mixture, along with the formation of hard compounds such as titanium oxides and nitrides. The depth of the remelted layer varied depending on the processing atmosphere, with the deepest and hardest layer observed for samples treated in air. All laser treatments substantially enhanced surface microhardness and dry sliding wear resistance compared to untreated samples. The most favorable combination of low friction, minimal wear, and surface uniformity was achieved with the argon-treated sample. In-vitro tests confirmed that all treated surfaces remained non-cytotoxic, supporting their potential for biomedical applications.