PSI - Issue 68

Mohamed Elsayed et al. / Procedia Structural Integrity 68 (2025) 1003–1009 Elsayed et al./ Structural Integrity Procedia 00 (2025) 000–000

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et al., 2021). Among the seven branches of AM techniques, laser powder bed fusion (LPBF) is widely used for producing metal components with complex geometries and high mechanical properties (Gong et al., 2021). Despite LPBF's advantages, fabricating large components is challenging, leading to the production of smaller parts that are later joined using welding techniques such as gas tungsten arc welding (GTAW) and laser welding (LW). (Huysmans et al., 2021) optimized GTAW parameters for joining 316L SS plates fabricated by LPBF, finding good weldability at 96 A current, 8 cm/min welding speed, and 12 L/min gas flow rate. Additionally, (Mohyla et al., 2020) reported that the hardness of the welded joints in the fusion zone (FZ) of AMed 316L SS is lower compared to the base metal (BM). Laser welding (LW) offers advantages over GTAW, particularly by using the same heat source as LPBF technique, creating a unified manufacturing process. (Feng et al., 2023) studied the impact of building orientations on the microstructure of LW joints in AMed 300M steel. The microstructural analysis revealed a cellular and columnar dendritic structure in the welded joints, closely resembling the BM. Furthermore, a columnar to equiaxed grains transition (CET) occurred in the FZ as the building orientation changed from 0° to 90°, attributed to increased cooling rates. (Mokhtari et al., 2021) studied the microstructure analysis of LW joints of AMed 316L SS. The study showed that the grain characteristics of the FZs were similar to BMs. Based on these findings, the welding technique significantly influences the microstructure of the FZ, which in turn affects mechanical properties of the welded joint such as the indentation resistance. Therefore, this study investigates the microstructure evolution and indentation characteristics of additively manufactured 316L stainless steel welded joints using GTAW and LW techniques across the BM, heat-affected zone, and FZ. BMs were fabricated via LPBF with 45° orientation angle. Nomenclature SS stainless steel FZ fusion zone AM additive manufacturing CET columnar to equiaxed transition LPBF laser powder bed fusion SLM selective laser melting GTAW gas tungsten arc welding Yb: YAG ytterbium-doped yttrium aluminum garnet LW laser welding LCSM laser confocal scanning microscope BM base metal 2. Materials and methods 1.1. Specimens manufacture and heat treatment The 316L SS plates were fabricated using the LPBF method by SLM 280 HL equipment with a 45° inclined orientation relative to the Z-axis, as shown in Fig. 1 (a). The dimensions of plates (BMs) are 60x70x2.5 mm 3 in length, width, and thickness, respectively. A 200 W (Yb: YAG) laser system as the heat source, with a scanning speed of 800 mm/s. A zig-zag hatching pattern with a 60° rotation angle was employed, as depicted in Fig. 1 (b). The hatch spacing was 120 µm, and the layer thickness was 30 µm. Argon gas was supplied with a flow rate of 7.5 m/s to prevent oxidation. The printed plates were then heat-treated at 1000°C for 60 minutes in a Nabertherm N41/H chamber furnace, followed by water quenching (Sohrabpoor et al., 2021). The energy density was approximately 69.44 J/mm³, calculated using Equation 1 (Mäkikangas et al., 2021), as follows: = " $ % ! $ & (1) Where E is the volumetric energy density (J/mm 3 ), P is the laser power (W), S is the laser scanning speed (mm/s), T is the layer thickness (µm), and H is the hatch space (mm).