## 3 Results  
### Impact of Parameters  
Porosity vs. Energy Density  
Hardness measurements revealed values ranging from 223 to 262 HV across different parameter sets, as shown in Figure 3a,b. The average hardness for as-printed specimens using optimal parameters was 254 HV in the XY plane and 250 HV in the XZ plane, indicating slight anisotropy. The difference in hardness values between the XY and XZ planes (\(\Delta\)HV) ranged from 2 to 25 units, with higher anisotropy generally observed at lower energy densities.  
Figure 2: Dimensions of small specimens used in tensile tests (Dimension in mm).  
This anisotropy can be attributed to the directional solidification inherent to the LPBF process, resulting in columnar grain structures aligned with the build direction. Specimens printed with parameters yielding higher cooling rates (higher scan speeds, lower energy densities) typically exhibited greater anisotropy, likely due to more pronounced columnar grain formation.  
The relationship between energy density and relative density (inversely related to porosity) was analyzed. Specimens printed with parameters yielding an energy density of 111 J/mm\({}^{3}\) (900 mm/s scan speed, 120 W laser power) achieved the highest relative density of 99.96%. At energy densities below 100 J/mm\({}^{3}\), lack-of-fusion defects dominated the microstructure, characterized by irregular, interconnected pores. Conversely, at energy densities exceeding 200 J/mm\({}^{3}\), keyhole porosity increased, manifested as spherical voids from entrapped gases during excessive melting.  
The energy density and porosity relationship did not follow a simple linear trend (Table 2), suggesting complex interactions between processing parameters. Parameters with similar energy densities but different combinations of power and speed sometimes yielded significantly different porosity levels, highlighting the limitations of using energy density as the sole optimization metric. However, it should be noted that the range 50-100 J/m\({}^{3}\) seems the best in terms of density and hardness.  
The analysis of the collected data reveals a clear correlation between the volumetric energy density (J) and the relative density and microhardness of the processed material. Optimal material properties are achieved within an energy density range of approximately 100 to 150 J/mm\({}^{3}\). In this window, samples consistently exhibit high relative densities (above 99.9%) and balanced microhardness values across the XY and XZ planes, indicating uniform and stable microstructures. As energy density increases beyond this range  
Figure 3: Porosity (**a**) and hardness in the XY plane (**b**) and XZ plane as a function of the power of the laser.  
(e.g., 200-240 J/mm\({}^{3}\)), a decline in relative density is observed, likely due to overheating, keyholing, or increased porosity. Conversely, too low of an energy input (<75 J/mm\({}^{3}\)) also results in lower densities and inconsistent hardness, suggesting insufficient melting. The hardness anisotropy (difference between the XY and XZ directions) generally increases with very high and very low energy inputs, highlighting the need for energy optimization to minimize directional property variation. Overall, samples processed at 900 mm/s with 120 W and a hatch distance width of 0.06 mm appear to offer the best balance between density and mechanical performance.