PSI - Issue 74

Kipkurui Ronoh et al. / Procedia Structural Integrity 74 (2025) 77–84 Kipkurui Ronoh / Stru ctural Integrity Procedia 00 (202 5 ) 000 – 000

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A sample's surface area of 2 × 2 mm 2 was ablated using cross- hatching patterning (45°/−45°) at room temperature and the laser parameters used are provided in Table 2. 2.3. S urface analysis The dry-cleaned ablated samples were subjected to X-ray photoelectron spectroscopy (XPS) (Axis Supra, Kratos Analytical Ltd, UK) to quantify the surface's elemental composition. Both survey and high-resolution spectra were collected in a binding energy range of 0 – 1200 eV using a pass energy of 80 eV and 20 eV, respectively. After XPS, the samples were ultrasonically cleaned in acetone and ethanol to remove remaining ablation residues. Scanning electron microscopy (SEM) images were obtained using Verios 460L SEM (FEI, Czech Republic) and MIRA SEM (Tescan, Czech Republic). A Dektak XT contact 3D mechanical profilometer (Bruker, USA) with nominal vertical and lateral resolutions of 0.1 nm and 0.5 μm, respectively, was used to obtain surface topography data. A 2 μm tip radius was used to scan a surface area of 300 × 3 00 μm² with width made up of 300 scanning lines. An automated X Y stage held the samples for the measurements. The collected data was analysed using the open-source Gwyddion 2.64 program. The contact angles were measured using the sessile droplet method (See System E, Advex Instruments, Czech Republic) at room temperature. A 2 μL drop let of high - purity (99.7 %) distilled water was manually dispensed onto the sample surfaces using a micropipette. The droplet images were captured with a high-definition camera, and the contact angles were determined by analysing droplet images using See Software 7.0. 3. Results and discussion 3.1. Morphological observations on the surfaces of the samples Fig. 1 presents representative SEM micrographs of polished and ablated surfaces of the three alloys following ablation at fluences of 1 and 10 J/cm 2 . The polished samples appeared smooth with a few scratch marks.

Fig. 1: SEM images of the polished and laser-ablated surfaces ablated by 1 and 10 J/cm 2 laser fluence and same scanning velocity of 100 mm/s, hatching distance of 5 µm and one scanning pass. A scale of 5 µm applies to all images

When samples are irradiated with a fluence above the threshold fluence, rough structures, called laser-induced surface structures, are produced and are influenced by process parameters. The laser-ablated samples shown in Fig. 1 exhibited laser-induced periodic surface structures (LIPSS). The LIPSS at 1 J/cm 2 were smooth, well-formed and