Laser polishing of additive manufactured CoCr components for controlling their wettability characteristics

Laser polishing treatment on 3D printed metal components has attracted great attention due to the potential applications in the dental implant and jewelry fields. In this study, cobalt-chromium (CoCr) alloys were polished over an area of 3 × 3 mm2 using a pulsed mode 70 W fiber laser. The micromorphology, composition, surface roughness and contact angles of the polished samples were characterized using a scanning electron microscope with energy-dispersive X-ray spectroscopy (SEM/EDX), optical profiler and contact angle goniometer, respectively. The results indicate that argon, with a median flow rate of 6.0 l/min, is the most feasible shielding gas for CoCr oxidation prevention, while maintaining a precise oxidation prevention control system. The object distance is found to be a critical parameter affecting the surface quality, and enhanced surface quality (Sa) ≤1 μm is achieved at a laser defocusing distance (Df) of +6 mm. Apart from laser power, other parameters in the laser polishing treatment, including scanning velocity, flow rate, object distance and hatching space, have a similar influence on surface roughness and contact angles. On a hydrophobic surface, the contact angle increases with an increase in surface roughness, due to the laser polishing variation of the CoCr surface with different defocusing distances. However, the contact angle decreases when the surface roughness of a hydrophilic surface increases, as in the laser polishing variation of the CoCr surface with different powers. Consequently, the wettability of laser treated CoCr seems more likely to be in the Wenzel's state.