The effect of colored titanium oxides on the color change on the surface of Ti-5Al-5Mo-5V-1Cr-1Fe alloy

In the present investigation, a color change on the surface of Ti-5Al-5Mo-5V-1Cr-1Fe alloy was studied through thermal oxidation experiments in the temperature range of 100-1000 °C with an interval of 50 °C. The phase composition and morphology of oxide layer were characterized by x-ray diffraction and light optical microscopy, respectively. The result shows that the achieved colors after thermal oxidation followed a chromatic scale which went from silver white to light yellow to golden yellow to blue and then to light green and brownish black. The color change on the alloy mainly resulted from the different colored titanium oxides in the oxide layer. The silver white, yellow, and blue on the alloy with the oxidation temperature below 600 °C were the results of TiO₂ white tint, TiO golden tint, and Ti ₂O₃ blue color, respectively. The light green was the mixed color of TiO golden tint and Ti₂O₃ blue color in the oxidation temperature range of 600-700 °C. However, at the oxidation temperatures exceeding 750 °C, the color turned to be brownish black. It might be associated with the thick, porous, and multilayered oxide layer. Consequently, it can be suggested that the illustration of the color change is vitally necessary for assessing the quality of the final workpieces according to the color change on titanium alloys.