PSI - Issue 74

Tomáš Vražina et al. / Procedia Structural Integrity 74 (2025) 106 –113 Tomáš Vražina / Structural Integrity Procedia 00 (202 5 ) 000 – 000

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3

2. Material and methods The 316L stainless steel used in this study was produced from two different powder batches (Table 1) using two distinct additive manufacturing technologies (Table 2). Both Commercially available powders have particle size typical for LPBF processing (15-45 µm). Vertically oriented flat specimens with cross-section dimension 4 mm and heigh 45 mm were fabricated using Renishaw and EOS systems. No postprocessing heat treatment was applied to the specimens. The relative densities were measured by the Archimedes method and found to be 99.2% in the case of Renishaw specimens and 99.4% for the EOS specimens. Small samples were extracted from each set of specimens for microstructural characterization. Scanning electron microscopy (SEM) (Fig. 1a, b) was performed on mechanically prepared samples, which were further polished electrolytically in a 10% oxalic acid solution for 45 seconds at 5 V. The samples were subsequently etched using a BERAHA II solution (800 ml distilled water, 400 ml HCl, and 48 g NH₄FHF) , to enhance the visibility of the cellular boundaries. The etched microstructure of the material is shown in Fig. 1a and 1b, highlighting the distinct features characteristic of the LPBF process. Additionally, thin foils were prepared for scanning transmission electron microscopy (STEM) to enable high-resolution observation of dislocation structures, as presented in Fig. 1c.

Table 1 Chemical composition of 316L powders in wt.% provided by the manufacturers Elements Cr Ni Mo C Si

Mn 1.2 1.9

S

N

Fe

EOS

18.3 18.3

14

2.7 2.2

-

0.47

-

0.1

Bal. Bal.

RENISHAW

11.2

0.02

1.1

0.004

0.03

Table 2. LPBF process parameters for manufacturing the 316L steel. Parameters Laser power [W] Scan speed [mm.s -1 ]

Jump speed [mm.s -1 ]

Scan strategy

Hatch distance [mm]

Layer thickness [mm]

EOS

214.2

928.1

-

Rotation (67°)

0.1

0.04

RENISHAW 0.05 Microstructural characterization was performed using a LYRA 3 XMU field emission SEM equipped with an electron backscatter diffraction (EBSD) system from Oxford Instruments. Grain size measurements were conducted using AZtecCrystal software, applying the Feret diameter method. The EBSD analysis covered an area of approximately 1800 μm × 1200 μm, providing average grain sizes of 49.8 μm for the Renishaw sample and 49.3 μm for the EOS sample. A JEOL JEM-2100F STEM was used to observe the dislocation structure in detail. The microscope is equipped with a bright-field detector, allowing for high-resolution imaging in scanning transmission electron microscopy mode. 200 - 5500 Chess board 0.06

Fig. 1. (a) Representative SEM micrograph of additively manufactured 316L (EOS) capturing the melt pool (b) the cellular substructure inside the melt pools (EOS) - SEM. (c) detail of dislocation cell walls (STEM BF)