## 3 Results and Discussion
Pore size analysis from the optical microscopy cross-sections indicates that most of the pores are actually much smaller than 10 micrometers (Figure 2c,f) and, thus, below the current resolution of the neutron microtomography datasets. However, the comparison of  
Figure 2: Comparison of the neutron microtomography (**a,d**) sections and their equivalent optical microscopy (**b,e**) sections. Graphs (**c,f**) show pore size distributions extracted from the full volume of the 3D neutron microtomography datasets and from a single slice of optical microscopy (**b,e**) sections, respectively. relative densities from the optical 2D section and the corresponding 2D slice of the 3D data (see Figure 2a-d) reveals that the contribution of pores smaller than 10 micrometers to the total relative density of the printed samples is negligible. Density values acquired from 2D optical microscopy (99.73% and 98.35% for Samples 1 and 2, respectively), and from the corresponding 2D slices of 3D neutron microtomography data (99.81% and 98.42% for Samples 1 and 2, respectively) are indeed very close. The difference in relative density with and without considering pores smaller than 10 micrometers in the equivalent diameter is less than 0.1%. It should be noted that in 2D optical microscopy cross-sections, there is a contribution of open porosity to what appears to be closed porosity; however, the provision of the 3D datasets reveals such artefacts. Figure 3 shows the 3D distribution of pores in Samples 1 and 2, with equivalent diameter color coding. Figure 3c,d give distributions from the top view, along the building direction, revealing pore locations with respect to the intended production volume. A strong correlation with the scanning strategy is observed. Although pores in Sample 1 are much more homogeneously distributed than in Sample 2, in both samples, most of the pores are located at specific surface regions corresponding to laser off events. Laser off events refer to the end of the scanning along each scan line, where the scanning speed changes to lower values before the laser is completely turned off, resulting in a local increase of heat input, causing material evaporation and porosity formation [45]. A larger fraction of pores appear, in particular, outside the intended sample production volume. This is much more pronounced in the case of Sample 2, manufactured with lower hatching distance and higher laser power (see Table 1). In Sample 1, this type of porosity is significantly lower and limited to 9% (10% volume-wise) of the total number of closed pores larger than 10 micrometers. By contrast, these amount to 52% (54% volume-wise) in Sample 2. However, in the jewelry and watch industries, part contours are post-processed with surface treatments to ensure mirror-polished surfaces. Our interest, therefore, mainly lies in the porosity within the target shape of the samples. Figure 3e,f represent the distribution of visualized pores at the surface of the target shape of the printed samples. The results indicate very few pores are found at the target surface of Sample 1. On Sample 2, significant porosity is revealed at the target surface. Considering the surface with the highest porosity in both samples, relative density at the surface for Sample 1 is 99.98%, whereas for sample 2, it is only about 99.60%. 3D analysis of pore morphologies in additively manufactured samples helps to distinguish different types of pores. Most of the pores in Samples 1 and 2 are close to spherical. These round pores (e.g., Figure 4a) form due to the injection of dissolved gas at the liquid-solid interface. Spherical pores typically have four different origins: (i) the moisture absorbed by the powder particles in the ambient atmosphere, (ii) shielding gas during the manufacturing process, (iii) gas entrapped inside the powder particles during the powder atomization process, and (iv) entrapment of the gas during the manufacturing process due to alloy vapors inside the molten pool [46; 47].