Preparation of micro/nano-structured ceramic coatings on Ti6Al4V alloy by plasma electrolytic oxidation process
(1. School of Mechanical Engineering, Sichuan University, Chengdu 610065, China;
2. Department of Materials Engineering, Sichuan Engineering Technical College, Deyang 618000, China;
3. Sichuan Laboratory of Engineering Aeronautical Materials Inspection and Die-forging Technology, Deyang 618000, China)
2. Department of Materials Engineering, Sichuan Engineering Technical College, Deyang 618000, China;
3. Sichuan Laboratory of Engineering Aeronautical Materials Inspection and Die-forging Technology, Deyang 618000, China)
Abstract: In order to improve the osseointegration and antibacterial activity of titanium alloys, micro/nano-structured ceramic coatings doped with antibacterial element F were prepared by plasma electrolytic oxidation (PEO) process on Ti6Al4V alloy in NaF electrolyte. The influence of NaF concentration (0.15-0.50 mol/L) on the PEO process, microstructure, phase composition, corrosion resistance and thickness of the coatings was investigated using scanning/transmission electron microscopy, energy dispersive spectroscopy, atomic force microscopy, X-ray diffractometer, and potentiodynamic polarization. The results demonstrated that Ti6Al4V alloy had low PEO voltage (less than 200 V) in NaF electrolyte, which decreased further as the NaF concentration increased. A micro/nano-structured coating with 10-15 μm pits and 200-800 nm pores was formed in NaF electrolyte; the morphology was different from the typical pancake structure obtained with other electrolytes. The coating formed in NaF electrolyte had low surface roughness and was thin (<4 μm). The NaF concentration had a small effect on the phase transition from metastable anatase phase to stable rutile phase, but greatly affected the corrosion resistance. In general, as the NaF concentration increased, the surface roughness, phase (anatase and rutile) contents, corrosion resistance, and thickness of the coating first increased and then decreased, reaching the maximum values at 0.25 mol/L NaF.
Key words: plasma electrolytic oxidation; Ti6Al4V alloy; micro/nano structure; NaF; surface modification