# Selective Laser-Melted Alloy 625: Optimization of Stress-Relieving and Aging Treatments
## 3 Results and Discussion  
### As-Built and Stress-Relived Conditions  
Figure 3 reports the micrographs of the selective laser-melted material in each plane obtained via light optical and scanning electron microscopy. XY is the scan plane, and it is perpendicular to the build direction Z. In the XY plane, the microstructural analysis showed the presence of elongated tracks of the melt pools with hatch angle rotation in the layer-stacking process equal to 60\({}^{\circ}\), as shown in Figure 3b. The micrographs related \begin{table}
\begin{tabular}{c c c} \hline  & **Contour** & **Inner Area (Islands)** \\ \hline Power [W] & 120 & 180 \\ Speed [mm/s] & 400 & 900 \\ \hline Spot size [\(\mu\)m] & 50 & 150 \\ \hline \end{tabular}
\end{table} 
Table 3: Laser parameters adopted for the contour and the inner area of the SLMed bars. to the ZX and YZ planes report melt pools stacked in the build direction with uniform orientation and shape (Figure 3c,d). The solidified microstructure is represented in the SEM micrographs of Figure 3e,f. Both cellular-shaped structures and elongated dendrites are present with different orientations. The melt pool boundaries are clearly highlighted by the chemical etching process in Figure 3, and they are denoted by dashed yellow lines in the SEM micrographs. The average values of the melt pool width and depth were measured using the micrographs of the as-built material. They resulted equal to 115 \(\upmu\)m and 220 \(\upmu\)m, respectively. Figure 3: Micrographs of the selective laser-melted material in the as-built condition obtained via light optical and scanning electron microscopy. Figure (**a**) reports an overview of the microstructural features on three perpendicular planes. The melt pools on the three planes are shown in (**b–d**). SEM observation of the melt pools are reported in (**e,f**): dendrites with different orientations are visible in (**f**). In SLMed alloy 625, the room-temperature mechanical properties obtained via the hardness and tensile tests in both the as-built and stress-relieved conditions are reported in Tables 4 and 5. In both the as-built and the stress-relieved conditions, the selective laser-melted alloy 625 is characterized by outstanding mechanical strength. In fact, it is significantly higher compared not only with the average literature properties of the conventionally manufactured material reported in Table 2 (wrought and centrifugally cast) but also compared to the minimum requirements defined by the ASTM B446-19 standard [12]. This strength increase is obtained at the expense of tensile deformability, which is reduced when compared to that of the conventional material. Moreover, in the stress-relieved condition, the percentage of elongation after fracture A% is lower than the minimum standard of the prescription. The mechanical properties in the as-built condition are compatible with the literature ranges reported in Table 2 for SLMed alloy 625. The ratio between yield strength and ultimate tensile strength is appreciably increased in the selective laser-melted material (0.70) compared to the literature data of both the wrought (0.45) and centrifugally cast (0.51) counterparts reported in Table 2. In addition, the mechanical performance of the selective laser-melted material is significantly better than that of the centrifugally cast version, as shown by the comparison with the literature data in Table 2.  
The susceptibility to intergranular corrosion was determined following the ASTM G-28 Method A standard [38] in both the as-built and stress-relieved conditions. The results were compared with those of the conventional wrought and soft-annealed material. In the as-built condition, the corrosion rate was equal to 0.38 mm/year after the 120 h corrosion test. Therefore, corrosion resistance in this condition is slightly higher than that measured by [PERSON] et al. [43] on the conventional wrought and soft-annealed material (0.65 mm/year). [PERSON] et al.