## 1 Introduction  
Powder bed fusion (PBF) is a type of additive manufacturing (AM) that involves the use of a laser or electron beam to melt and fuse layers of powdered material together to create a three-dimensional object [1, 2]. In PBF, a layer of powder is spread across a built platform, and the laser or electron beam selectively melts and fuses the powder together according to a digital model of the object being printed. Once the first layer is complete, another layer of powder is spread on top, and the process is repeated until the object is fully printed [3, 4, 5]. There are several types of PBF processes, including selective laser sintering (SLS), selective laser melting (SLM), and electron beam melting (EBM). These processes differ in the type of energy source used to melt the powder and the way in which the powder is delivered to the build platform [6, 7]. Laser-based powder bed fusion of metals (PBF-LB/M) uses a high-powered laser beam to melt and fuse powdered materials, typically metal alloys. A thin layer of powder is spread over a build platform and selectively melted by the laser beam according to a 3D computer-aided design model. The build platform is then lowered by a distance equal to the layer thickness, and the process is repeated with the next layer of powder. This process is repeated layer by layer until the object is complete. One of the key advantages of PBF-LB/M is its ability to produce complex geometries with high precision and accuracy. This is due to the high resolution of the laser beam, which can be focused to a spot size of a few tens of microns, allowing for the creation of intricate details and fine features. Additionally, the PBF-LB/M process can produce objects with a high density, as the melted powder is rapidly cooled and solidified, resulting in a strong and dense final product [8,9]. Cobalt-chromium-molybdenum (Co-Cr-Mo) is one of the alloys used in the PBF-LB/M process. The Co-Cr-Mo alloy is a well-known biomaterial used in medical applications due to its excellent mechanical properties, including high strength, good fatigue resistance, biocompatibility, and corrosion resistance. The PBF-LB/M of the Co-Cr-Mo alloy has been shown to have great potential for intricate and precise fabrication of complex shapes, which is particularly advantageous for producing personalized and patient-specific biomedical implants like joint replacements and dental implants. The PBF-LB/M Co-Cr-Mo alloy is also used in aerospace, automotive, tooling and machinery applications [10]. For example, it can be used to manufacture intricate turbine blades and engine components, or it can also be utilized in cutting tools to benefit from the alloy's high hardness and resistance to abrasion, allowing for extended tool life and improved efficiency. Although several papers have been published on the microstructure and mechanical properties of cobalt-chromium alloys manufactured by PBF additive manufacturing [11, 12, 13, 14, 15], the study of the tribological performance of the alloy is rare. [PERSON] et al. [16] studied the wear resistance of the Co-Cr alloy manufactured by SLM for dental applications. They used a biaxial chewing simulator for the wear tests at a constant load, with alumina ceramic as the counter material and deionized water as the lubricant. Their results suggest that SLM-CoCr is highly wear-resistant and could be an alternative for manufacturing prosthetic restorations, even in areas with occlusal loading. However, the effect of different working conditions and the morphology of the wear track of the alloy have not been studied. In another study, [PERSON] et al. [17] investigated the tribological performance of Co-Cr-Mo alloys fabricated by casting and SLM under dry and wet conditions. The tribological properties were evaluated using a reciprocating wear tester, with artificial saliva solution used for the lubricated tests at room temperature.