Coloring of titanium through laser oxidation: comparative study with anodizing

Surface oxidation of titanium was performed by cw-Nd:YAG laser (λ=1.064 μm) treatment in air. Different colors of the samples were obtained by varying the beam scan velocity. At the optical microscope, the samples showed a pattern of two-color bands. Compositional analyses performed by grazing incidence X-ray diffractometry, Raman spectroscopy, and secondary ion mass spectrometry revealed the formation of a titanium oxide coating that consisted of a mixture of polycrystalline oxide phases (Ti2O, TiO, Ti2O3 and TiO2). The refractive index and the thickness of the transparent oxide surface layer, as well as the chromaticity coordinates, were calculated from the reflectance spectrum of the samples. In order to elucidate the origin of the samples color, the properties of the laser-oxidized samples were compared with those of anodized ones with similar colors. The comparison allowed to conclude that the color was formed in all cases by light interference phenomena within the transparent oxide surface layer, which in the case of laser treated samples was only the thin outer zone of the titanium oxidized layer.