## 4 Discussion  
### Processing Parameter Optimization and Energy Density Effects  
The processing parameters employed for Nickel Alloy HX demonstrate significant optimization compared to the literature values for nickel-based superalloys processed via LPBF (Table 4). The energy density of 111 J/mm\({}^{3}\) falls within the optimal range identified by [PERSON] et al. [16] for nickel-based superalloys, avoiding excessive thermal input that can lead to keyhole formation, residual stress accumulation, and microstructural degradation. This moderate energy density approach contrasts with the higher values (>150 J/mm\({}^{3}\)) reported for Inconel 718 [17], which often result in increased thermal gradients and subsequent anisotropy.  
The scan speed of 900 mm/s aligns with the recommendations of [PERSON] et al. [18], who demonstrated that higher scan speeds (>800 mm/s) reduce thermal accumulation while maintaining adequate overlap ratios. This parameter selection is particularly significant as it enables rapid processing while ensuring complete powder melting and minimal heat-affected zone formation. The laser power of 120 W represents a conservative approach compared to studies by [PERSON] et al. [19], who utilized powers up to 285 W for Inconel 718, which often resulted in increased sputter formation and surface roughness.  
The high relative density achieved with Nickel Alloy HX (99.8%) demonstrates the effectiveness of the optimized parameter set, exceeding values reported for most nickel-based superalloys in the literature.  
Powder characteristics critically influence LPBF processing of nickel-based superalloys like EOS Nickel Alloy HX in aerospace applications. Spherical powder morphology with a particle size distribution of 15-45 \(\upmu\)m ensures optimal flowability and packing density, directly affecting layer uniformity and required laser energy density parameters [15].  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Material** & **Reference** & **Laser Power** & **Scan Speed** & **Layer** & **Energy Density** & **Relative** \\  & & **(W)** & **(mm/s)** & **Thickness (\(\upmu\)m)** & **(J/mm\({}^{3}\))** & **Density (\%)** \\ \hline EOS & This study & 120 & 900 & 30 & 111 & 99.8 \\ Nickel Alloy HX & [17] & 195 & 1200 & 30 & 103 & 99.2 \\ Hastelloy X & [18] & 180 & 800 & 40 & 117 & 98.8 \\ Hastelloy X & [20] & 150 & 1000 & 30 & 125 & 99.1 \\ Inconel 718 & [19] & 285 & 960 & 40 & 175 & 99.4 \\ Inconel 718 & [21] & 195 & 1200 & 25 & 129 & 99.6 \\ Inconel 625 & [16] & 195 & 650 & 30 & 167 & 99.3 \\ CM247 LC & [22] & 200 & 400 & 30 & 397 & 98.5 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Processing parameters comparison for LPBF nickel-based superalloys.  
Poor powder flowability necessitates reduced scanning speeds and increased laser power to achieve full densification, while irregular particle shapes promote gas entrapment, leading to increased porosity levels exceeding 1% [23]. Powder recycling in LPBF processes increases oxygen content and satellite particle formation, resulting in oxide inclusions that act as crack-initiation sites, reducing tensile strength by up to 10% and significantly degrading fatigue performance in Hastelloy components [24]. The connection between powder quality and LPBF parameters is essential for achieving porosity levels below the 0.2% required for aerospace applications, where minor defects can reduce significantly the elongation and induce brittleness in the material.