Combined effects of nanosecond laser-induced surface oxidation and nanostructure formation for selective colorization of nickel surfaces
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Metal surfaces can be nanostructured by laser irradiation making use of different effects ranging from thin film generation to nanostructures formation. Here, the colorization of pure nickel surfaces by nanosecond laser irradiation in air is demonstrated and studied in detail. Correlations between chromaticity coordinates and laser-processing parameter show that the accumulated fluence is the dominating factor in creation of a specific colored surface. The color of the laser-irradiated surfaces shows both angle-dependent and angle-independent in reliance on the processing conditions. The examination of the laser-colored surface demonstrates that lateral and vertical organized, laser-induced structures with nano-, micro-, and mesoscopic scales can be found simultaneously which contribute to the colorization in a particular manner. A comprehensive analysis of the processes involved in the color formation at nickel was performed by examining the surfaces by SEM, reflectometry, XPS, and XRD to verify the multi-process mechanisms of color formation. The most saturated colors result from interference effects within the redeposited layers. It was found that controlling the hatching distance applying optimized laser fluence enables a wider color range and allows a very precise setting of the color. Based on the extracted laser-processing parameters, the surface coloration of arbitrary pattern with desired optical properties becomes practicable, and nanosecond laser color marking can, therefore, be expanded to potentially new applications.
Authors are very grateful to Mr. Hirsch, Dr. Gerlach, and Dr. Frost for the assistance in XPS, XRD, and AFM, analysis, and discussion these results. Authors are also thankful to Mr. Zagoranskiy and Mr. Bayer offering meaningful experimental support for this work.
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