## Results and Discussion
### Microstructure Analysis  
The as-built state of the Inconel 939 alloy exhibits a typical nickel superalloy microstructure, featuring visible melt pools with dendritic structures growing across them. In the XY plane, melt pools are visible with a 67\({}^{\circ}\) rotation between layers (Figure 6A). In the XZ plane, the melt pools are uniform, indicating correct process parameters with no keyhole, under-melted, or balling melt pools, which confirms that the right parameters have been chosen (Figure 6B). The dendritic structures can be seen. Figure 5: Inconel 939 Rm and Rp0.2 values for as-built, HT1, and HT2 states at elevated temperature. \begin{table}
\begin{tabular}{l c c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**23 \({}^{\circ}\)C**} & \multicolumn{4}{c}{**700 \({}^{\circ}\)C**} \\ \cline{2-9}  & \multicolumn{2}{c}{**Yield Strength [MPa]**} & \multicolumn{2}{c}{**UTS [MPa]**} & \multicolumn{2}{c}{**Yield Strength [MPa]**} & \multicolumn{2}{c}{**UTS [MPa]**} \\ \cline{2-9}  & **Horizontal** & **Vertical** & **Horizontal** & **Vertical** & **Horizontal** & **Vertical** & **Horizontal** & **Vertical** \\ \hline EOS as-built & 880.0 & 740.0 & 1160.0 & 1090.0 & - & - & - & - \\ \hline
**As-built** & 909.3 & 788.3 & 1186.4 & 993.6 & 807.5 & 809.7 & 867.1 & 934.9 \\ \hline EOS heat-treated & 1130.0 & 1100.0 & 1520.0 & 1500.0 & 860.0 & 910.0 & 1050.0 & 1050.0 \\ \hline
**HT1** & 956.7 & 879.7 & 1428.5 & 1313.0 & 680.5 & 791.3 & 681.5 & 970.9 \\ \hline
**HT2** & 938.9 & 827.8 & 1394.9 & 1251.9 & 672.5 & 754.3 & 678.1 & 817.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Tensile tests yield strength and UTS values of as-built, HT1, and HT2 specimens at 23 degrees and 700 degrees Celsius with manufacturer’s data [11]. After the HT1 heat treatment, the microstructure shows elongated grains in the XZ plane and regular grains in the XY plane (Figure 6C,D), characteristic of LPBF nickel superalloys post-heat treatment. The dendritic structures are no longer visible. Black spots can be seen on the optical microscope, which have been identified using SEM as MC carbides, as they are rich in Nb, Ti, and Ta (Figure 7A-C), even though no increase in carbon has been measured. This can be due to the high mistake certainty of EDS in the case of oxygen and carbon. [PERSON] et al. (2024) [16] also detected regions with high concentrations of Nb, Ti, and Ta, with no increase in carbon on EDS. They identified those regions as MC carbides using TEM; therefore, it can be assumed that in the case of Inconel 939, all EDS-detected regions with high concentrations of Nb, Ti, and Ta are MC carbides. Precipitates were observed both on grain boundaries and intragranularly. Light-gray \(\gamma^{\prime}\) precipitates were also visible (Figure 7B). The HT2 heat treatment results in recrystallized grains, similar in size in both the XY and XZ planes (Figure 6E,F). The grains are more regular compared to the HT1 state but are highly elongated in the Z-axis. This can contribute to poorer tensile performance at elevated temperatures along the X-axis, as observed by [PERSON] et al. (2022) [14]. Larger grain areas in the \(\underline{X}\)-axis facilitate dislocation movement, causing easier crack nucleation and propagation. The precipitates remain in similar positions as in the case of the HT1 state, but because of grain growth, a high amount of precipitates is present intragranularly. This is caused by the lack of movement of the carbide nuclei after the LPBF process, as explained by [PERSON] et al. (2016) [17] (Figure 7D-F). The precipitates were again identified as MC carbides, as they show high Nb, Ti, and Ta concentrations. \(\gamma^{\prime}\) precipitates appear as light-gray round spots. Figure 6: Microstructures of Inconel 939 in as-built (**A**,**B**), HT1 (**C**,**D**), and HT2 (**E**,**F**) states.