# Process Parameter Optimisation in Laser Powder Bed Fusion of Duplex Stainless Steel 2205
## 5 Results and Discussion  
With the chosen values, it is necessary to experimentally check the optimal mechanical behavior of the specimens. To this end, SLM specimens have been manufactured using the chosen parameters. They have been heat-treated and tested. The results for the DSS-2205 obtained by additive manufacturing, both heat-treated (DSS-SLM-TT) and as-built (DSS-SLM-AB), are shown in Table 7. Despite the DSS-SLM-AB having a higher \(\sigma_{\text{uts}}\) and \(\sigma_{0.2}\), its \(\epsilon_{\text{r}}\) and A are far worse than those of the DSS-SLM-TT. This is the reason for the heat treatment because these are the properties to maximize. Figure 7 compares the engineering stress-strain curve of the reference base material (DSS-MB), DSS-SLM-TT, and DSS-SLM-AB, where it is easier to observe the differences in elongation between specimens (one single specimen per condition). The fracture surface of the different specimens was observed with SEM. Comparing Figures 8 and 9, the difference between the brittle behavior of DSS-SLM-AB and the ductile behavior of DSS-SLM-TT is clearly visible. In Figure 8, the mechanisms of brittle fracture can be clearly observed throughout the fracture section, resulting in minimal necking of the specimen. Conversely, in Figure 9, ductile fracture mechanisms in the form of microvoids can be seen, as well as necking of the specimen in the fracture zone. This same behavior is reproduced in the base material DSS-BM (Figure 10). The most remarkable difference is the shape of the necking; in DSS-SLM-TT, the neck is circular, indicating isotropic behavior, whereas in DSS-BM, the neck is elliptical, indicating anisotropic behavior due to the grain orientation caused by the hot rolling process. If the microstructure of the DSS-SLM-TT specimen is analyzed, the two phases of a duplex steel can be easily observed in Figure 11: the dark phase is ferrite, and the light phase is austenite. The microstructure phases have been measured by image analysis, using \begin{table}
\begin{tabular}{l c c c c c} \hline \hline  & **Density (\%)** & \(\sigma_{0.2}\) **(MPa)** & \(\sigma_{\text{uts}}\) **(MPa)** & \(\epsilon_{\text{r}}\) **(\%)** & **A (\%)** \\ \hline DSS-SLM-TT & 99.82 & 526 & 795 & 55.01 & 80.49 \\ \hline DSS-SLM-AB & – & 953 & 1098 & 14.28 & 59.09 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Properties of DSS-2205 manufactured with optimal parameters. Figure 6: Parameter optimization based on S* and P* [H* = 1]. the software Leica--L.A.S. V4.12 for metallographic phase analysis. Figure 11 also shows the microstructure of the DSS-BM, in which a clear directionality of the austenite phase is observed, caused by the productive process of hot rolling. In the case of DSS-SLM-TT, it has been possible to achieve an austenite content of 35.91% by quenching at 1050 \({}^{\circ}\)C and quenching in water. Aiming to increase the content of the austenitic phase in the DSS-SLM microstructure and to maximise the \(\epsilon_{\mathrm{r}}\) and \(A\), the effect of quenching temperature between the range of 975 \({}^{\circ}\)C to 1100 \({}^{\circ}\)C was analyzed based on  
Figure 8: Fracture surface of the DSS-SLM-AB: (**a**) magnitude 4.8\(\times\), (**b**) magnitude 200\(\times\). Figure 9: Fracture surface of the DSS-SLM-TT: (**a**) magnitude \(10\times\), (**b**) magnitude \(200\times\). Figure 10: Fracture surface of the DSS-BM: (**a**) magnitude \(2\times\), (**b**) magnitude \(300\times\). Figure 11: Microstructure of the (**a**) DSS-BM and (**b**) DSS-SLM-TT. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline Temperature & \multirow{2}{*}{\%\_Austenite} & \multirow{2}{*}{\(\sigma_{\text{D2}}\) (MPa)} & \multirow{2}{*}{\(\sigma_{\text{uts}}\) (MPa)} & \multirow{2}{*}{\(\varepsilon_{\text{f}}\) (\%)} & \multirow{2}{*}{A (\%)} \\ \cline{1-1}  
In this article, the mechanical properties prioritized are the elongation at fracture (\(\epsilon_{\tau}\)) and the reduction of area (A).