Nanosecond pulsed laser cleaning of titanium alloy oxide films: Modeling and experiments

Abstract

Nanosecond pulsed laser cleaning is an indispensable green technology. A three-dimensional (3-D) finite element model (FEM) was used to predict the surface temperature during laser cleaning. Then, the macroscopic morphology of the FEM that was obtained was verified using digital ultra-depth-of-field microscopy (OM). Finally, the variation in the surface morphology with the maximum power density (F), x-axis spot overlap ratio (Ux), and y-axis spot overlap ratio (Uy) was determined using field-emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). The change in surface composition was analysed using X-ray photoelectron spectroscopy (XPS), and optical emission spectroscopy (OES) was used to monitor laser cleaning. Transmission electron microscopy (TEM) was used to analyse the surface secondary oxidation thickness. The original surface consisted of titanium oxides (Ti4+ and Ti3+) and organics. The Ti0 peak was enhanced, and the O content was reduced after laser cleaning. Therefore, the laser-cleaning effect was clear. The surface was smooth without cracks when the maximum power density and the spot overlap ratio were set to 31.85 MW/cm2 and 80 %, respectively. A dense and uniformity oxide film, 29 nm thickness, was formed on the surface of TA15 titanium alloy after laser cleaning. Changes in F, Ux, and Uy caused noticeable changes in the Ti I and Ti II peaks in the OES spectra, which were used to monitor laser cleaning.