Laser-induced coloring of titanium alloy using ultraviolet nanosecond pulses scanning technology

Abstract

This paper presents the laser-induced coloring of commercial titanium alloy (Grade 5) sheets using nanosecond-duration pulsed ultraviolet laser (355 nm) scanning technology in an atmospheric environment. This study evaluated the effect of different scanning speeds and pitches of cross-hatch scanning paths parameters on optical properties and chemical composition of the titanium alloy sheets. The optical properties, surface morphology, and surface chemical composition characteristics of the titanium alloy (Grade 5) sheets depended on the laser irradiation conditions. The characteristics of the samples were systematically analyzed using an ultraviolet–visible/near-infrared spectrophotometer, an X-ray photoelectron spectroscope, and an optical microscope. The experimental results indicated that the reflectance spectra decreased as the laser scanning speed decreased from 100 to 25 mm/s. From the CIE 1931 diagram, the color changes in the optical microscopy images were consistent. The atomic content of oxygen increased with decreases in the scanning speed. When the scanning speed was decreased, the binding energy decreased from 530.4 eV to 529.5 eV and was attributed to the TiO bond in TiO2. In the oxidation layer thickness analysis that decreased greatly with increasing the hatching distances and scan speeds. When the scan speed and hatching distance of 25 mm/s and 5 μm that cause the thermal accumulation; therefore, the largest oxidation thickness approximately 1000 nm. The titanium alloy sheet main ingredient (i.e. titanium (Ti), aluminum (Al), and vanadium (V)) proportion was decreased that depending on different laser-induced coloring parameters. Moreover, the carbon (C) and oxygen (O) concentration that depended on the scan speeds and hatching distance. While the oxygen concentration increased with the scan speed decreasing.