## 3 Results and Discussions  
The morphology of the powder used for PBF-LB/M printing is shown in Figure 1a. The powder has a particle size range of 15 \(\upmu\)m to 45 \(\upmu\)m. Figure 1b shows the microstructure of the PBF-LB/M Co-Cr-Mo alloy. During PBF-LB/M, the laser melts the powder and creates a melt pool, which is the region of molten metal that solidifies to form the final part. The melt pool boundaries are the regions where the molten metal transitions to the solid phase. These boundaries can be observed in Figure 1b. One common defect in PBF-LB/M parts is lack of fusion (LoF), which occurs when the laser fails to completely melt and fuse adjacent layers of powder particles together. LoF can occur due to insufficient laser power, slow scanning speed, or insufficient powder bed preheating. When LoF occurs, the unmelted or partially melted powder particles can create voids or cracks in the final part, reducing its strength and integrity [21; 22]. In this research, the optimum PBF-LB/M process parameters recommended by Renishaw were used for printing the samples; however, regions with LoF and pores can still be observed in the samples. The SLM-printed samples had an average surface roughness (Ra) of 7.3578 \(\pm\) 0.1384 \(\upmu\)m and a density of 8125 \(\pm\) 36.22 kg/m\({}^{3}\). They had an average yield strength of 693 \(\pm\) 12 MPa and an ultimate tensile strength of 1096 \(\pm\) 15 MPa with elongation at break of 18% \(\pm\) 2%. Figure 2 shows the microhardness profiles of printed samples along the wear track and through the thickness. These data can be used to investigate changes in the mechanical properties of the material due to variations in the processing parameters or thermal history. The results show a quite uniform hardness profile with an average microhardness of 409.67 HV through the thickness and 404.05 HV along the wear track. Figure 1: (**a**) Morphology of the Co-Cr-Mo powder, (**b**) Melt pool boundaries and lack of fusion of as-printed Co-Cr-Mo alloy samples. It is worth pointing out that the build direction of the samples was through the thickness in this research. The reason for the slightly higher hardness through the thickness of the SLM-printed samples could be the fact that the heat transfer during the PBF-LB/M process is different in the build direction compared to the other directions. In the PBF-LB/M process, heat is primarily applied to the top surface of the powder bed through the laser beam. This concentrated heat source melts and fuses the powder, causing the material to solidify as the heat dissipates from the top layers downward. Consequently, the cooling rate in the build direction may vary, potentially affecting the microstructure, including grain size. In some cases, a slower cooling rate can lead to the formation of larger grains, which can have implications for material properties. Larger grain sizes are often associated with changes in microhardness values, although the exact relationship can depend on various factors, including material composition and processing parameters. Additionally,  
Figure 2: Hardness profiles of as-printed samples (**a**) through the thickness, and (**b**) along the wear track. the residual stresses within the material can be different in the build direction compared to the other directions, which can also affect the microhardness [23; 24]. Figure 3 shows the average coefficient of friction (COF) for SLM-printed samples tested under different loads and sliding frequencies. Mobil Gear SHC 150 (Synthetic gear oil) was used for the lubricated test results presented in Figure 3. It can be observed that in both dry and lubricated contacts, as the applied normal load increases, COF decreases. At higher loads, there is an increase in the contact area between the two surfaces in contact, which can lead to a decrease in the localized pressure and shear stresses in the contact area. This can result in a decrease in the frictional resistance between the two surfaces, as the deformation and adhesion at the interface are reduced [25].