Flash plasma electrolytic oxidation and electrochemical behaviour in physiological media of additive manufacturing Ti6Al4V alloy
(1. Departamento de Ingeniería Química y de Materiales, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, 28040 Madrid, Spain;
2. CIDETEC, Basque Research and Technology Alliance (BRTA), Po. Miramón 196, 20014 Donostia-San Sebastián, Spain;
3. Departamento Matemática Aplicada, Ciencia e Ingeniería de Materiales y Tecnología Electrónica, Universidad Rey Juan Carlos, C/Tulipán s/n, Móstoles 28933, Madrid, Spain)
2. CIDETEC, Basque Research and Technology Alliance (BRTA), Po. Miramón 196, 20014 Donostia-San Sebastián, Spain;
3. Departamento Matemática Aplicada, Ciencia e Ingeniería de Materiales y Tecnología Electrónica, Universidad Rey Juan Carlos, C/Tulipán s/n, Móstoles 28933, Madrid, Spain)
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 mm) 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.
Key words: additive manufacturing; laser powder bed fusion; plasma electrolytic oxidation; Flash-PEO; titanium; crevice corrosion; α-MEM