Corrosion Behavior of Selective Laser Melting (SLM) Manufactured Ti6Al4V Alloy in Saline and BCS Solution

The frequency of surgeries involving the use of metal implants in orthopedic medicine to replace degenerative or fractured joints is increasing, and it is therefore important to optimize the lifespan and quality of these implants. Advances in additive manufacturing (AM), or 3D printing, are creating new opportunities to personalize implants in ways that reduce mechanical stress at the joint implant interface and improve bone ingrowth and implant stability; however, it is not well understood if and to what degree the AM process alters the corrosion behavior of the materials it produces. In this study, six Ti6Al4V prints manufactured via a selective laser melting (SLM) method were examined regarding their corrosion behavior in both saline and bovine calf serum (BCS) solutions. E_corr and I_corr values were comparable between the CM-Ti6Al4V control and SLM-EDM surfaces; however, SLM surfaces were found to have more narrow passivation behavior evidenced by significant decreases in E_pass values relative to CM-Ti6Al4V. We believe this is a consequence of microstructural differences between CM-Ti6Al4V and SLM-Ti6Al4V. Specifically, the SLM-Ti6Al4V demonstrated a dominant α' martensitic microstructure and decreased vanadium-rich β-phase. BCS solution had a detrimental effect on potential parameters, E_corr and OCP, decreasing these values relative to their saline counterparts. Increased surface roughness of the SLM-printed surface seemed to amplify the effects of the BCS solution. Furthermore, modest decreases in E_pass and I_pass were observed in BCS solution, suggesting that the presence of protein may also interfere with passivation behavior. These findings have implications for how SLM-Ti6Al4V implants will perform in vivo and could possibly influence implant longevity and performance.