High-temperature stability and decoding of large field-of-view observable color codes prepared by femtosecond laser on titanium alloy

This study reported on the large field-of-view observable color code obtained by femtosecond laser-induced oxidation on titanium alloy. The simulation results showed that simultaneous roughening of the oxide layer and metal layer could effectively increase the color rendering range of the structural colors. Based on the diffraction effect of the diaphragm, the laser energy was periodically distributed. In addition, the simultaneous formation of the oxide layer and the micro/nano structures was attributed to the periodic distribution of laser energy. Compared to the substrate, the increase in oxygen content of the colored area ranged from 5 % to 11 %, indicating that the infiltration of oxygen inside the material was increased. Additionally, the surface chemical composition of the upper oxide layer of the colored areas was TiO₂. XRD analysis showed that laser-induced surface coloring did not affect the phase composition of the alloy except for the generation of a small amount of carbon. Moreover, different scanning numbers affected the color difference ΔE∗ ab of adjacent scanning speeds. High-temperature experiments showed that the color code prepared by femtosecond laser-induced oxidization of titanium alloy was reliable in use at less than 100 °C. Since the color code could still be clearly obtained at a field angle of 77.3°, the angle insensitivity of the color code could be effectively improved by selective roughening of the oxide layer prepared by femtosecond laser. Furthermore, the decoding of color code was the inverse encoding process. Therefore, the angle insensitivity of the color code was improved and the temperature range of the structural color was clarified.