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Influence of Processing Gas Composition on Laser Colouring of Commercially Pure Titanium
N.Y. Khafaji, A.G. Demir, Z.A. Taha and B. Previtali

Laser induced thermal oxidation for colouring of commercially pure Ti (Grade II) is studied. Laser colouring was applied with a ns-pulsed Yb-fiber laser operating at wavelength of 1064 nm and with a pulse duration of 250 ns. The process gas composition was controlled by mixing an inert gas (Ar) with O2 in different proportions and compared to processing in ambient air. The results were analysed in terms of colour appearance as a function of different laser parameters and surface quality parameters, namely surface roughness and crack size. Chemical composition as well as corrosion behaviour were analysed for a comprehensive characterisation of the oxide layers. It has been observed that compared to working in ambient atmosphere, the use of the inert/reactive gas mixture flow induces a wider range of colours in the same laser parameter range, and generates fewer surface cracks and lower roughness.

Keywords: Fibre laser, titanium, Ti, inert/reactive gas mixture, colouring, surface roughness, crack, interference colours

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