## 3 Results and Discussion  
Figure 2 presents the \(\mu\)CT images of the Ni-Cr-Mo alloys produced by the three different approaches. The LWC alloy, produced by the vacuum casting technique [4],  
Figure 1: Schematic diagram of three manufacturing processes (lower) using single spherical Ni–Cr–Mo alloy (upper, SEM image, magnification = 250\(\times\)) for specimen preparation: LWC (**a**), SLM (**b**), and SMM (**c**). showed a relatively pore-free image. Meanwhile, a high number of large and small pores were evenly distributed inside the SLM and SMM alloys, respectively. The OM images of the Ni-Cr-Mo alloys are shown in Figure 3, where the results are comparable to the \(\mu\)CT results (Figure 2). The LWC alloy exhibited only a small number of pores, while the SLM alloy showed a lack-of-fusion porosity caused by insufficient penetration of the melt pool into the previous layer [19; 20]. To minimize this lack-of-fusion porosity, the SLM process conditions, including the beam speed, layer thickness, and hatch spacing, should be further optimized [19]. The SMM alloy showed the formation of a high number of small and round-shaped pores, due to plastic deformation from the powder metallurgy process [21]. The density analysis also showed a higher density for the LWC alloy (8.42 g/cm\({}^{3}\)) when compared to the SLM (6.87 g/cm\({}^{3}\)) and SMM (7.62 g/cm\({}^{3}\)) alloys. Figure 4 presents the XRD spectra for the Ni-Cr-Mo alloys. The XRD pattern revealed that all of the alloys were composed of a \(\gamma\) (face-centered cubic, FCC)-phased matrix, suggesting a solid solution of Ni [22]. The higher peaks exhibited by the SLM alloy may be explained by the higher crystallinity of the SLM specimens when compared to the LWC specimens. A slight shift of the (111) plane was observed in the SMM alloy, indicating a decreased cell size due to the low Mo concentration in the alloy [23]. Only the SMM alloy showed the formation of (Mo,Cr)C carbide with an \(\varepsilon\) (hexagonal close-packed, HCP) phase. It is already known that carbide precipitation increases the strength parameters of an alloy [24]. Figure 3: Optical microscopy images (magnification = 50\(\times\)) of Ni–Cr–Mo alloys: LWC (**a**), SLM (**b**), and SMM (**c**). Red arrow in (**b**) indicates SLM building direction. Figure 2: \(\mu\)CT images of Ni–Cr–Mo alloys: LWC (**a**), SLM (**b**), and SMM (**c**). Cylindrical-shaped 3D images (left), cylindrical-shaped images with cut planes (middle), and top images of cylinders (right). The EDS maps for the Ni-Cr-Mo alloys are presented in Figure 5. The maps for the LWC alloy showed segregation of the Cr and Mo elements along the grain boundaries during solidification [25]. The Ni, Cr, and Mo elements were also more homogeneously distributed in the SLM and SMM alloys than in the LWC alloy. Figure 6 shows the EBSD images of the Ni-Cr-Mo alloys produced by the three different methods. The BC and IPF maps showed finer grains for the SLM and SMM alloys when compared to the LWC alloy, due to the different heating and cooling conditions of the SLM and SMM alloys. In particular, the IPF map for the SLM alloy showed ultrafine grains, which were caused by the high-temperature gradients involved in the SLM process [22]. Moreover, the phase map for the SMM alloy revealed the precipitation of carbide, confirming the XRD results (Figure 4). Figure 4: XRD spectra of Ni–Cr–Mo alloys: LWC (**a**), SLM (**b**), and SMM (**c**). Peaks corresponding to \(\gamma\) matrix and \(\varepsilon\) carbide phases were identified by ICDD card no. 03-065-6291 and 00-001-1188, respectively. Black arrow in SMM alloy (**c**) indicates shift of (111) plane. Figure 5: EDS images of Ni–Cr–Mo alloys (magnification = \(100\times\)): LWC (**a**), SLM (**b**), and SMM (**c**). Table 1 summarizes the mechanical property results for the Ni-Cr-Mo alloys. The porosity has a crucial impact on the final material properties and performance [18].