This study aims to induce a laser-induced periodic surface structure (LIPSS) on different coatings using a pico-second laser. An energy dispersive X-ray (EDX) spectroscopy analysis was performed, and wettability and friction tests were performed. Additionally, the surface electric field intensity (EFI) distribution was analyzed using the finite element method (FEM) to study LIPSS generation on different coating morphologies. The EDX results demonstrated that the LIPSS induced on the TiN coatings did not destroy them; however, the TiCN coatings were oxidized in the LIPSS fabrication process. The numerical simulation results indicated that the surface EFI and depth of the surface roughness were significantly linear, and the EFI was significantly related to the refractive index and extinction coefficient of the coating material. The wettability and friction test results implied that the LIPSS on different coatings could exhibit super hydrophilicity and played a role in friction reduction.

A fundamental study of the mechanisms of generation of the laser-induced periodic surface structure (LIPSS) includes electromagnetic deposition theories and matter reorganization theories. The proposed two-dimensional finite element model incorporates frequency-domain electric field analysis and the two-temperature model (TTM) to simulate the growth process of LIPPS in multi-pulse picosecond laser irradiation. The proposed simulation proceeds as follows: the electric field intensity (EFI) distribution is calculated by referring to the material surface morphology and determines heat distribution by the electromagnetic heating (EMH); the heat distribution is introduced into the TTM to calculate the electron and lattice temperatures; by comparing the lattice and the vaporization temperature, material ablation is determined to obtain a new surface topography and single-pulse simulation completes; and by introducing the new surface topography recursively, multi-pulse laser irradiation can be simulated. In the calculation of a picosecond laser with a wavelength of 1064 nm, pulse duration of 20 ps and different laser fluences for the irradiation of the Ti6Al4V alloy surface, this method could simulate the ripple-like distributed EFI, and a surface morphology similar to that of LIPSS grew after several pulses. The results were in agreement with the observed experimental results. The proposed assumption is a novel approach for the explanation of the LIPSS generation mechanism.

In biomedical engineering, laser-induced periodic surface structures (LIPSSs) have been extensively applied where laser irradiation of selective laser-melted (SLMed) samples to generate LIPSS-covered free-form samples is a promising technique. Using this technique, nanopillars around a spheroidal particle that was not molten during the SLM process have been formed, indicating that nanopillars can be induced around spheroidal particles on a material surface. This study investigates the mechanism of LIPSS and nanopillar formation on SLMed and uneven surfaces experimentally and through finite-difference time-domain simulation. A 50 Hz picosecond laser with 1064 nm fixed wavelengt, 20 ps pulse duration, 0.5 J/cm2 laser fluence, and 400 mu m/s scanning speed was employed to irradiate Ti6Al4V alloy samples with 100 mu s exposure time. The results show that induced nanopillars form a concentric area around a single particle with curvature radius approximately twice the particle radius. The simulated electric field intensity is ripple-like distributed for particle size beyond 5 mu m, with approximately 1 mu m periodic length and is close to the laser wavelength. This matches the experimental results from scanning electron microscopy for 800-00 nm LIPSS periodic length, indicating that desired nanostructures can be generated by appropriately designing the surface topography before laser irradiation.

The goal of this study was to investigate a study for the efficient generation of pillar-like nanostructure (nanopillar) on a material surface over a large area. In this research, a vertical cross-scanning (VCS) strategy using two linearly-polarized lasers with different laser conditions was proposed for the generation of nanopillars on a mirror-polished surface on a large scale. It found that the laser fluence and scanning speed of the second laser scanning should be controlled within a specific range to generate the nanopillars. Additionally, the distance between scan lines, which is defined as hatch distance, h, of the second scan, is also a non-negligible factor to induce nanopillars to cover the entire surface. This work demonstrated that the VCS method is a feasible strategy for the fabrication of nanopillars on the entire mirror-polished surface of Ti6Al4V alloy by linearly-polarized picosecond laser conveniently and efficiently.