Laser marking and coloration of Ti-6Al-4V with ultrashort pulses

Abstract

A routine for color marking using oxide layers and laser-induced periodic surface structures is presented. Titanium and alloys thereof are marked with pixelated graphics at a high resolution with tempering colors. A computational approach for the laser path calculation enables a fast-forward marking of complex designs. The color map attained from a laser parameter studies enables vivid coloration. The minimal color pixel size is given by the optical setup and laser wavelength at near-infrared and green radiation to the focal spot size. A pixel size of 35 and 20 μ m was reached within this study, and no cross talk and distinctness between adjacent colors were observed. The oxide layer growth is sensitive on the applied laser strategy and parameter setting; however, a set of stable coloration conditions is conceived. Hitherto, fine color nuances in blue unravel the unique potential of this approach by oxidizing the substrate leading to a defined oxide layer thickness at a high repetition rate below the threshold fluence. Additionally, ultrashort pulsed laser pulses below 10 ps enable the generation of laser-induced periodic surface structures. In the low spatial frequency regime, these structures are correlated with the polarization direction of the laser light. Afterward, diffraction gratings with rotated spatial periodicity are manufactured using a half-wave plate. This allows forgery-proof marking strategies, where both mechanisms could be superimposed to increase the information density and complicating counterfeit product labeling.