Study on laser coloring and color erasing-rewriting of TC4 surface

In this work, different colors with a large variation in total color difference (ΔE*) were induced by 1064 nm nanosecond pulsed laser on TC4 titanium alloy, which can expand and systematize the color gamut on TC4. The influences of laser parameters on the color difference were evaluated by hand-held colorimeter with CIEL*a*b* color space quantitatively and the morphology of oxide thin film was characterized. With the increasing of scanning speed, ΔE* increased from 22.8 to 95.72 and lightness difference (ΔL*) increased from 13 to 78. With the increasing of laser power, ΔL* decreased gradually. With the increasing of pulse repetition frequency, ΔE* increased from 15.07 to 98.42, and ΔL* increased from -9 to 74. Finally, the experiment of color erasing and repairing in controllable processing atmosphere was carried out as well. The ΔE* before and after laser erasing is less than 7 in low oxygen environment by introducing nitrogen atmosphere, and being exposed to liquids, which indicates that colors can be erased and repaired based on laser induced reduction. Rewriting in the erased fields can increase the saturation and lightness of colors. The possibility of erasing or rewriting colors in special treatment environment would take laser coloring to a new level, allowing not only improvement of color quality from reprocessed fields but also modification of marks during the laser processing according to the wishes of operators.