Nanosecond pulsed laser irradiation of titanium: Oxide growth and effects on underlying metal

• Laser-stimulated surface oxidation of titanium forms color markings.
• Oxide thickness, microstructure, phase and composition are characterized.
• Reflectance and chromaticity are determined.
• Substrate structure and composition are examined.

Titanium oxide/oxynitride coatings were created on the polished surface of commercially pure, grade 2 titanium substrates by irradiating samples in air using a nanosecond-pulsed, infrared (1064 nm) fiber laser. Coatings consist of three distinct layers, including a thin TiO2 rutile cap, a TiO middle layer, and an inhomogeneous bottom layer that is composed of TiOxN1 − x and possibly oxygen-intercalated phases such as Ti6O. The combined thickness of TiO2 and TiO layers was varied from ~ 10 to 120 nm by increasing the accumulated laser fluence. Laser-grown coatings exhibit different colors, which vary with oxide thickness. The observed color is attributed to the interference of incident white light reflected from the upper and lower boundaries of the TiO2 capping layer.