## 3 Results  
### As-Built LPBF Micrographs  
\[E_{\
u}=\frac{L_{P}}{D_{s}\cdot v_{s}\cdot y_{s}}\left[J/mm^{3}\right]. \tag{1}\]  
The volumetric energy density (E\({}_{\
u}\)) equation as expressed in Equation (1) above highlights the inter-relation between the key process parameters such as the laser power (L\({}_{\text{p}}\)), layer thickness (D\({}_{\text{s}}\)), scanning speed (V\({}_{\text{s}}\)), and hatch distance (y\({}_{\text{s}}\)). This served as the basis for the parametric design employed in this study. The as-printed cubes were generally dense (\(\geq\)99.6%) with the most dense  
Figure 1: SEM micrographs: (**a**) morphology of the gas atomized G-NiCu30 Nb (DIN 2.4365) powder; (**b**) etched powder particle revealing dendrite structures. cubes recording a relative density of 99.8%, as shown in Figure 2. Table 2 below highlights the process parameters and the achieved relative densities in each print set. For the 80 \(\upmu\)m hatch distance print set, the least and most dense cubes recorded relative densities of 99.63% and 99. 80%, respectively. These represented percentage porosities of 0.37% and 0.20%, respectively. Similarly, in the 140 \(\upmu\)m hatch distance print set, 99.71% and 99.80% were recorded as the lowest and highest relative densities, respectively. This also accounted for percentage porosities of 0.29% and 0.20%, respectively. From Figure 2, for both hatch distance print sets (80 \(\upmu\)m and 140 \(\upmu\)m), small spherical pores can be observed, which are characteristically gas-induced pores which may have been trapped during melting and solidification [22]. The average pore size measured with the ANSYS Pro image analysis software among all the samples was less than 1 \(\upmu\)m. In Figure 3, micrographs of 80 \(\upmu\)m hatch distance samples at different scanning speeds are compared. The as-built cube printed at 1000 mm/s scanning speed shown in Figure 3a is observed to be denser and crack-free compared to Figure 3d, printed at 1500 mm/s scanning speed, which shows more cracks. Calculated energy density values ranged from 55-88 J/mm\({}^{3}\). Since the volumetric energy density (Ev) is the same for the samples shown in Figure 2d,h (about 56 J/ mm\({}^{3}\)), and the cracks do not resemble Lack of Fusion (LOF) defects, they are believed to be residual stress propagating cracks arising from the build-up of large amounts of local residual stress in the as-built condition due to the generally high temperature gradient associated with the LPBF process. High scanning speeds tend to generate higher cooling rates [23], which, in combination with smaller hatching distance, can lead to local stresses and fracture when the material ultimate tensile strength is \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Sample** & **Laser Power** & **Layer Thickness** & **Scanning Speed** & **Hatch Distance** & **Relative Density (\%)** \\ \hline
2a & 200 & 30 & 1000 & 80 & 99.80 \\
2b & 200 & 30 & 1200 & 80 & 99.72 \\
2c & 200 & 30 & 1400 & 80 & 99.63 \\
2d & 200 & 30 & 1500 & 80 & 99.70 \\
2e & 200 & 30 & 550 & 140 & 99.78 \\
2f & 200 & 30 & 650 & 140 & 99.77 \\
2g & 200 & 30 & 750 & 140 & 99.71 \\
2h & 200 & 30 & 850 & 140 & 99.80 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Process parameters and the respective relative densities of the as-built cubes shown in Figure 2.  
Figure 2: Light optical microscope (LOM) micrographs showing two different hatch distances with scanning speed variation at constant laser power (200 W) and layer thickness (30 \(\upmu\)m) for unetched as-built cubes; the highest relative density of 99.8% was recorded at 1000 mm/s and 850 mm/s. exceeded [24]. The increase in scanning speed to 1500 mm/s is, therefore, believed to have induced higher cooling rates which influenced residual stress build-up and led to fracture or cracks as seen in Figure 3e,f and not in Figure 3a-c at 1000 mm/s scanning speed. The micrographs in Figure 4 show etched and unetched cubes at different magnifications built using a 140 \(\upmu\)m hatch distance.