Influence of surface finishing and heat treatments on the corrosion resistance of LPBF-produced Ti-6Al-4V alloy for biomedical applications

Additive manufacturing (AM) technologies are gaining increasing attraction for biomedical applications due to the granted customizability and optimal surface topography for osteointegration. Ti-6Al-4V is one of the most promising materials due to its biocompatibility. However, excessive ions release can occur, leading to a relevant immunologic response in the surrounding tissues. Despite the corrosion behavior of the conventionally -manufactured material being well known, it should be assessed for AM-processed components, as the effect of the unique superficial and microstructural features granted by the process is still quite unknown. The aim of this paper is the electrochemical evaluation of the passive current density of the laser powder bed fusion (LPBF)-processed Ti-6Al-4V alloy via potentiostatic tests, carried out at typical in-service potentials for biomedical implants. This parameter is correlated with the ion release rate of the alloy, a fundamental phenomenon to address to prevent possible inflammations caused by the implant. Different manufacturing conditions (surface finishing, heat treatment) and exposure time (0, 60 and 6000 h) were considered. The importance of performing these measurements over a long period (> 8 months) was demonstrated. In fact, despite the initial current densities being significantly affected by the surface and microstructural differences, the ion release rates converged for long-time exposures. The results also underlined the good corrosion resistance of the material. Poor corrosion performances, alongside with significant current densities development, were observed in the as -built condition. A pickling treatment demonstrated to mitigate such effect without compromising the unique surface finishing granted by the manufacturing technology.