# Design and Assessment of an Austenitic Stainless Alloy for Laser Powder Bed Additive Manufacturing
## 2 Materials and Methods  
The powder of the selected alloy was manufactured externally by LERMPS UTBM using gas atomization under argon atmosphere. Particle size was assessed using a laser granulometer Malvern Mastersizer 3000 (Malvern Panalytical, Malvern, UK), with a gas pressure of 3.5 bars. The particle size ranges from d\({}_{10}\) = 11 \(\upmu\)m to d\({}_{90}\) = 40 \(\upmu\)m, with a median value of d\({}_{50}\) = 22 \(\upmu\)m. Using a ProX200 LPBF machine (3D Systems, Rock Hill, SC, USA), cubic (10 \(\times\) 10 \(\times\) 10 mm) and rectangular specimens (42 \(\times\) 14 \(\times\) 4 mm) for tensile tests were fabricated on a 316L stainless steel substrate. A near-infrared laser source (\(\uplambda=1064\) nm) was used. The hatching distance was set to 60 \(\upmu\)m and the powder layer thickness was 30 \(\upmu\)m. The scanning strategy was 45\({}^{\circ}\)/225\({}^{\circ}\) relative to the orthogonal axis of the substrate. The focal distance was \(-6.0\) mm. Specimens were arranged in staggered rows on the building platform, with a building sequence oriented in the opposite direction of the Ar gas flow to prevent sputter deposition. All processing conditions were based on ranges optimized for 316L [25] to evaluate the robustness of the new alloy. Cubic test pieces were produced using two scan speeds (v) of 1000 mm/s and 1200 mm/s, with the laser power (P) gradually increased from 120 W to 250 W in increments of 6 W (+2%). As a first indicator of material quality, the surface roughness of the top surface was assessed using optical microscopy. Surface roughness is typically correlated with porosity, as both are usually associated with lack of fusion or unstable melt flow [26]. This technique has proven successful in a previous study for the rapid evaluation of new alloys via LPBF. Using this method, the optimal surface roughness was achieved with a laser power of 144 W and a scan speed of 1200 mm/s, and these parameters were used for the remainder of the study. The chemical composition of the powder and samples produced by LPBF was measured by inductively coupled plasma optical emission spectroscopy ICP-OES. The carbon content was measured by combustion infrared absorption (CIR). The values are listed in Table 1, showing some difference in the powder composition from the nominal values, especially with slightly lower amounts of some alloying elements, like Co and Al. The Co content further decreases slightly after LPBF processing. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**wt. \%** & **Fe** & **Cr** & **Ni** & **Mn** & **Co** & **Al** & **C** \\ \hline Nominal & 42 & 15.2 & 13.7 & 11.7 & 15 & 2.3 & 0.02 \\ \hline Powder & 45.9 & 14.3 & 13.1 & 11 & 13.5 & 2.1 & 0.0064 \\ \hline LPBF build & 42.5 & 15.2 & 14.2 & 13.9 & 12 & 2.1 & 0.0064 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Composition of the selected optimized alloy. Microstructure observations were conducted on a scanning electron microscope (SEM) Zeiss SUPRA55 VP (Zeiss, Oberkochen, Germany) operated at 20 kV in backscattered electrons (BSE) mode and for Electron Back-Scattered Diffraction (EBSD) mapping. Variations in chemical composition were assessed using Energy Dispersive X-ray Spectrometry (EDX) mapping, with an Oxford SDD detector XmaxN 80 (Oxford Instruments, Abingdon-on-Thames, UK). No significant variations in chemical composition were detected within the limits of the EDX technique, indicating the absence of major compositional variations in the microstructure. However, it is possible that minor variations not detectable by this technique may still be present. Phase identification was accomplished using an X-ray Diffractometer (XRD) X'Pert Pro MPD Panalytical (Philips/Panalytical, Malvern, UK) with Cu K\(\alpha\) radiation operated at 40 mA and 45 kV. Divergence slits at 0.5\({}^{\circ}\) were set for the incident beam and a graphite monochromator with a Miniprop point detector were used for the diffracted beam.