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Materials Science in Additive Manufacturing SLM of ODS steel: Process and properties

Table 1. Chemical composition of the base ferritic/ were carried out at a load of 10 N with a dwell time of 5 s.
martensitic steel Uniaxial tensile tests were performed on three specimens
for each condition to determine the tensile strength, YS,
Element C Si Mn Cr Ni Mo Nb V P Fe and relative elongation of the specimens. The specimens’
wt. % 0.12 0.2 0.2 12.1 0.1 1.3 0.35 0.2 0.001 Bal.
blank parts were initially printed, heat-treated, and then
machined. These tests were performed under ambient
Table 2. Process parameters of selective laser melting conditions using a Zwick/Roell z100 tensile testing
machine. Tensile testing at an elevated temperature of
Parameters Range 720 ± 10°C was carried out using a Zwick/Roell z050
Laser power 150 – 225 W machine (ZwickRoell GmbH & Co., Ulm, Germany). For
Scanning speed 420 – 820 mm/s all the specimens, tests were carried out under a crosshead
Hatch distance 120 μm displacement velocity of 0.8 mm/min on the elastic section,
Layer thickness 30 μm and 2 mm/min on the plastic section. An examination of
the fractured surfaces from the tensile tests was conducted
using SEM.
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by high-temperature annealing at 720°C for 60 – 180 min.
In the present study, the heat treatment was performed in a 3. Results and discussion
vacuum at 1050°C for 30 min with subsequent quenching,
followed by high-temperature annealing at 720°C for 3.1. Material preparation
60 min. The heat treatment process was carried out using a The application of acoustic mixing facilitated the
vacuum furnace Carbolite Gero LHTW 200 – 300/22-1G production of steel powder with a spherical morphology
(Carbolite Gero Ltd., Derbyshire, UK). and uniformly distributed oxide particles on the surface, as
demonstrated by the SEM image (Figure 1). The presence
2.3. Characterization of nanosized oxides on the particle surfaces resulted in
Subsequent to the printing process, the samples were a slight reduction in the powder’s flowability, from 12
separated from the platform by wire-cut electrical s/50 g to 16 s/50 g. Zhai et al. reported the flowability
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discharge machining. The estimation of the density of all of ODS 316L-Y O steel powder was not decreased after
2
3
samples was performed by the Archimedes method. Cubic low-energy ball milling. Nevertheless, the outcome can
samples with dimensions of 10 mm × 10 mm × 10 mm be ascribed to the diminished wettability and flowability
were prepared for microstructural investigations, phase of Y O , which, being located on the surface of the base
2
3
composition analysis, and microhardness testing. The material particles, predictably reduces the flowability of
samples were pressed into epoxy resin and then subjected the obtained material. However, flowability remains for
to grinding and mechanical polishing. Porosity and inner utilization in the SLM process.
defects fraction were calculated of the pore fraction in
relation to the whole image plane using ImageJ image 3.2. The influence of SLM process parameters on
analysis software on optical microscope images with ×50 relative density
magnification. The grain size estimation was performed The effects of laser power and scanning speed on relative
using optical micrographs along the building direction. density are presented in Figure 2. Laser power varied in the
Phase analysis was conducted using a Bruker D8 range from 150 to 225 W. As the laser power increases, the
Advance X-ray diffractometer (XRD; Bruker Corporation, relative density increases until it reaches a threshold value
Billerica, MA, USA) with Cu-Kα radiation (a = 1.5418 Å) of VED. In general, the density of samples fabricated using
in the range 2θ = 30° – 100°. A scanning interval of 0.02° laser powers of 200 W and 225 W is higher compared to
was used. Before microstructural analysis, the specimens those produced with laser powers of 150 W and 175 W.
were etched using a 3:1 solution of hydrochloric acid Scanning speed varied in the range from 420 to 820 mm/s.
and nitric acid. The microstructural characterization was Contrary to the influence of laser power, increasing
carried out utilizing a Leica DMI5000 optical microscope scanning speed resulted in lower density. A similar
(Leica Microsystems GmbH, Wetzlar, Germany) and a tendency has been observed in another study. 31
Tescan Mira3 LMU scanning electron microscope (SEM) When samples were fabricated without platform pre-
(TESCAN GROUP, Brno, Czech Republic). heating, all of them exhibited horizontal surface cracks,
The hardness of the samples was evaluated using a caused by thermal stresses arising from high temperature
Buehler Micromet 5103 hardness tester (Buehler Ltd., gradients during the SLM process. To address this issue, a
USA) employing the Vickers hardness method. The tests set of samples was fabricated using a platform pre-heating

Volume 4 Issue 1 (2025) 4 doi: 10.36922/MSAM025060004