PSI - Issue 74

Jaromír Brůža et al. / Procedia Structural Integrity 74 (2025) 1–8 Jaromír Brůža / Structural Integrity Procedia 00 (2025 ) 000–000

3

3

2.2. Additive manufacturing The L-PBF manufacturing of the EOS and Praxair powders was performed using an EOS M 290 printer. The SLM powder was consolidated using an SLM 125HL printing system as described elsewhere (Laleh et al., 2021). The fabrication process was performed under a high-purity argon environment with a maximum tolerance for oxygen of 1%. The default processing parameters listed in Table 2 were adopted for the manufacturing of cuboidal 10×10×10 mm 3 samples from Praxair and EOS powders. It is important to note that these parameters were optimized for each L -PBF machine to produce highly dense specimens with a relative density of over 99.5 %, which was verified via Archimedes' method using a Sartorius Quintix 224-1S precision balance. A meander hatching pattern with a rotation of 67° between subsequent layers was used in all prints as seen in Fig. 1. During the manufacturing of samples, the building platform was preheated to 80 °C in the case of EOS and Praxair powders, while the SLM print was performed with a preheating of 200 °C. The volumetric energy density listed in Table 2 was calculated according to Eq. 1 and serves as a rough estimate of input energy.

Table 2: Processing parameters of fabricated specimens

Processing parameters

P [W] 214.2

v [mm/s]

t [mm]

h [mm]

VED [J/mm 3 ]

EOS; Praxair

928.1

0.04 0.03

0.1

57.7

SLM

175

400

0.12

121.5

t h v P ⋅ ⋅

[J mm ] 3

(1)

VED

=

2.3. Microstructure characterization Samples were mechanically ground and polished following the standard metallographic procedures down to 0.25 µm diamond paste and finished with 0.04 µm oxide polishing suspension for 8 minutes. Specimen surface preparation was finalized by electrolytic polishing using 10 % oxalic acid solution for 45 seconds under 5 V at room temperature. For characterization of microstructure, grain morphology , and texture, a scanning electron microscope (SEM) Tescan LYRA 3 XMH FEG/SEMxFIB equipped with an Oxford Instruments Symmetry electron backscatter diffraction (EBSD) detector was used at a workin g distance of ~10 mm, and acceleration voltage of 15kV and 20kV for SEM images and EBSD, respectively. For large EBSD maps (1500×1000 µm) and details (360×240 µm), a step size of 1 µm and 0.25 µm, respectively, was chosen , while an exposure time of 5 ms was identical for both types of maps. To reveal site-specific nano-scale chemical heterogeneity corresponding to the microstructure, several FIB (focused ion beam) foils were taken at different positions within an individual melt pool. The chemical mapping within areas of interest was subsequently performed by a ThermoFisher Scientific Talos F200i transmission electron microscope in scanning mode (STEM) , operated at 200 kV and equipped with a sensitive EDS (energy -dispersive X-ray spectroscopy) detector with a large collection angle, operating in Velox Software, enabling accurate elemental quantification. 2.4. Hardness measurements The Vickers hardness of L - PBF 316L steels was determined by a ZHV30 Vickers ZwickRoell tester using a load force of 1 kgf and a dwell time of 10 s. For hardness measurements, specimen surfaces were mechanically polished down to 1 µm diamond paste. The average value and standard deviation were calculated from at least 10 indentations on metallographic sections taken parallel and perpendicu lar to the building direction for each variant of L-PBF 316L steel.