PSI - Issue 74

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

78 2

2023; Tatiana et al., 2023). Nickel-based super-alloys are commonly used in aerospace, petrochemical and marine industries (Special Metals, 2005; VDM Metals, 2024), while the iron-based super-alloys are commonly employed in electrical heating elements for industrial furnaces and household appliances. This study focuses on the three alloys: MONEL® alloy 400 (a NiCu substitutional solid solution alloy), VDM® Alloy 699 XA (a NiCrAl alloy known for metal dusting resistance) and Kanthal® AF (a FeCrAl alloy known for its corrosion resistance). Lasers have revolutionised modern manufacturing by enabling precise, efficient, and versatile material processing (Corsaro et al., 2024). Their high energy density facilitates surface modifications with minimal material waste and thermal damage (Biffi et al., 2023). Ultrafast laser ablation, which uses extremely short, high intensity pulses, enables accurate micro- and nanostructuring with minimal thermal damage (cold ablation) and controlled surface chemistry (Primus et al., 2023). This makes it ideal for advanced applications, including micro-processing, while also modifying surface topography, surface chemistry, and wettability of metallic alloys (Biffi et al., 2023; M. A. Khan et al., 2024). The wetting behaviour of the surfaces is influenced by both topography and surface chemistry (M. A. Khan et al., 2024; Ronoh et al., 2024b). Ultrafast laser ablation alters these properties by creating rough textures and modifying surface chemical composition through reduction of surface free energy, both of which enhance (super)hydrophobicity by influencing liquid–surface interactions . The hydrophobic surface has a contact angle, θ of 90° ≤ θ < 150° while superhydrophobic surface has θ of 150° ≤ θ ≤ 180° (Mohamed et al., 2015). Initially, laser ablation produces high energy metal oxides, which undergo a time-dependent shift toward (super)hydrophobic states upon atmospheric exposure. Since laser-induced wettability depends on processing parameters, understanding their influence is key to tailoring hydrophobic properties in metallic alloys. Hence, the purpose of the study is to examine the influence of laser fluence and hatching distances on the surface morphology, surface chemistry and wettability of the laser-ablated surfaces of superalloys. The findings aim to advance knowledge on the wetting behaviour of laser-ablated metallic surfaces aimed at enhanced corrosion control. 2. Materials and methods 2.1. Materials Three alloys were selected for this study. Each specimen, measuring 10 × 10 × 1 mm, was subjected to grinding and polishing to achieve a mirror-like finish. The samples were then cleaned ultrasonically with acetone and ethanol for 20 minutes. The chemical compositions of the samples are shown in Table 1.

Table 1: Nominal chemical composition (wt.%) of the alloys. Alloys Ni Cr Al Fe Nb

Cu

Si

Ti

C

Mn

699 XA

64.30 28.00 2.60 2.50

0.50 0.50

0.50 0.60 0.10 0.50

MONEL® alloy 400 63.68

2.50

31.00 0.50

0.30 2.00 0.08 0.40

Kanthal® AF

22.00 5.30 71.52

0.70

2.2. Laser ablation experiments An ultrafast laser micromachining system (Perla®100, Hilase, Czech Republic) was employed (Ronoh et al., 2023). The samples were raster scanned using a scanning head (intelliSCAN 14, Scanlab, Germany), mounted on a x − y translation stage. A linearly polari sed beam was focused to 25 μm spot size using F−θ lens (Linos, Qioptiq, Germany).

Table 2: Laser processing parameters used in the experiment Parameters

Levels

Laser Fluence, F [J/cm 2 ] Scanning Velocity, V [mm/s] Hatching Distance, H [µm] Number of Scanning Pass(es), n

1

4

8

10

100

200

400

800 100

5 1

20

50

2

4

8