## 2 Materials and Methods
### Printing Parameters  
Prior to printing of the samples for magnetic measurements, printing parameters were determined for printing bulk samples from the Fe-Si-Cr powder with low porosity (up to 2%) and no visible macroscopic defects (visible cracks, delaminations or uneven growth). Default printing parameters of stainless steel 316 L for the Realizer SLM-50 printer were chosen as initial values of printing parameters (Table 2), resulting in printed samples with high porosity and macroscopic cracking. Next, a laser re-melting strategy was adopted for improving the printer material quality, as it enables the incremental melting of the powder: laser re-melting involves scanning each layer or the surface of the printed material twice, before applying the next layer of fresh power on the bed. Several studies have demonstrated improved density and surface quality with the strategy for SLM [18; 19; 20]. Printing of cubical \(8\times 8\times 8\) mm samples was performed to investigate different combinations of laser power and scanning speed on both the primary and secondary scans, layer thickness and hatch distance were constant throughout the study. The parameters of the study were limited to 50-75 W/75-100 W (primary/secondary scan) for the laser power and 1 m/s/0.5-2 m/s for the scanning velocity. Higher energy input (resulting in higher laser power or lower scanning velocity) was not investigated as it resulted in extensive sputtering (primary scan) or macroscopic cracking. The printing parameters employed for achieving the highest relative density of 98% with the least cracking \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Elements** & **Fe** & **Si** & **Cr** \\ \hline Wt \% & Balance & 4 & 1.3 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of powder characterization. Figure 2: (**a**) Scanning electron microscope (SEM) magnification of the investigated powder, (**b**) Powder particle size distribution and percentage of particles below a specific particle size. are presented in Table 2 alongside the initial parameters. The structure of the printed samples was evaluated with standard metallographic practices with polishing and optical microscopy. The porosity was determined from the processing of thresholded images. The average sample absolute density of 7340 kg/m\({}^{3}\) was measured with the Archimedes scale method. Next, toroidal samples exhibiting a rectangular cross section of \(5\times 5\) mm, inner diameter of 50 mm and outer diameter of 60 mm were printed for magnetic measurements as shown on Figure 3a-c.  
Two powder coating related issues were met when advancing from cubical to toroidal samples:  
* Uneven growth (Figure 3d)--due powder balling, the uneven growth resulted in inferior density of the printed part, distorted part dimensions and printing termination, if growth is prominent enough to restrict the re-coater movements. Uneven powder deposition on the part was determined as the main cause for this issue, which was solved by double re-coater swiping to brush away the excess powder. Even growth of the printed part also seemed to be promoted by the laser re-melting strategy, as incremental melting of each layer seemed helpful for eliminating emerging irregularities; and
* Delaminations (Figure 3e)--were the result of excessive powder deposition on the printed part. It occurred when operating the printer without a feeder mechanism (suitable for parts with low height) and adding powder to the build chamber manually during an interrupt in the printing process. In that case, the build platform needed to be raised slightly manually after adding the extra powder, until only a thin coating of powder is visible on the printed part.