Cracks growth behaviors of commercial pure titanium under nanosecond laser irradiation for formation of nanostructure-covered microstructures (with sub-5-μm)

This study reported on the formation of sub-5-mu m microstructures covered on titanium by cracks growth under 10-ns laser radiation at the wavelength of 532 nm and its induced light modification for production of nanostructures. The electric field intensity and laser power density absorbed by commercial pure titanium were computed to investigate the self-trapping introduced by cracks and the effect of surface morphology on laser propagation characteristics. It is found that nanostructures can form at the surface with the curvature radius below 20 mu m. Meanwhile, variable laser fluences were applied to explore the evolution of cracks on commercial pure titanium with or without melt as spot overlap number increased. Experimental study was first performed at the peak laser fluence of 1.063 J/cm(2) to investigate the microstructures induced only by cracks growth. The results demonstrated that angular microstructures with size between 1.68 mu m nd 4.74 mu m was obtained and no nanostructure covered. Then, at the peak laser fluence of 2.126 J/cm(2), there were some nanostructures covered on the melt induced curved microstructured surface. However, surface molten material submerged in the most of cracks at the spot overlap number of 744, where the old cracks disappeared. The results indicated that there was too much molten material and melting time at the peak laser fluence of 2.126 j/cm(2), which was not suitable for obtainment of perfect micro-nano structures. On this basis, peak laser fluence was reduced down to 1.595 J/cm(2) and the sharp sub-5 mu m microstructures with nanostructures covered was obtained at spot overlap number of 3720. (C) 2016 Published by Elsevier B.V.