Characterisation of bioactive films on Ti-6Al-4V alloy

In an attempt to increase the bioactivity and corrosion resistance of a Ti-6Al-4V alloy, the plasma electrolytic oxidation (PEO) process for surface modification was utilised. Selected samples were subjected to further treatment, either thermal or alkali. The morphology, chemical composition and phase composition of the ground and treated Ti-6Al-4V alloy substrates were investigated using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). It was observed that during the anodic process under sparking discharge conditions, the simultaneous incorporation of calcium and phosphorus in the forming oxide layer occurs. The resulting layers were porous and exhibited the typical morphology for layers formed during the PEO process. After the alkali treatment of samples oxidised at 140 V, a gel-like titanate layer was formed. The bioactivity investigations in simulated body fluid (SBF) solution and with human bone marrow stromal cells (MSCs) indicated that after anodising at 140 V and following alkali treatment the Ti-6Al-4V alloy exhibits osteoinductive properties. The electrochemical investigations showed that application of the anodising process of the Ti-6Al-4V alloy significantly improved its corrosion resistance in Ringer solution. The samples anodised at 80 V presented the highest corrosion resistance because of the formation of the thin, compact oxide layer on the alloy surface.