Flash plasma electrolytic oxidation and electrochemical behaviour in physiological media of additive manufacturing Ti6Al4V alloy

Abstract

The objective of this work is to understand the plasma electrolytic oxidation (PEO) treatment and electrochemical behaviour of a Ti6Al4V alloy manufactured by a laser powder bed fusion additive manufacturing (AM) technique known as direct metal laser sintering (DMLS). Ca and P-containing coatings were produced with short time (<120 s) PEO treatments (also termed as Flash-PEO) obtaining 3–10 μm-thick coatings on both the AM alloy and a conventional counterpart. Subsequently, the electrochemical behaviour of the bare and treated alloys was assessed in a modified α-MEM solution via potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The fine α-lamellar microstructure of the AM alloy with small β-phase particles at the interlamellar spaces was seen to advance the onset of sparking promoting faster growth of PEO coating in comparison to the conventional alloy. Flash-PEO coatings enhanced the corrosion protection of both conventional and AM alloys, the thinnest (<3 μm) coatings providing up to three times greater protection. AM Ti6Al4V was found to be susceptible to localized crevice corrosion which could be assigned to the high grain boundary density. Flash-PEO treatments, even as short as 35 s, were sufficient to successfully prevent it.