Plasma electrolytic oxidation of Zr-Ti-Nb alloy in phosphate-formate-EDTA electrolyte

·Fine pore, bioactive oxide coatings with superior corrosion resistance were obtained on Zr-Ti-Nb alloy via PEO treatment.·EDTA combined with an organic source of calcium enables the incorporation of calcium into the oxide coating from stable and clear electrolytes.·EDTA-based electrolyte led to improvements in the overall productivity and reproducibility of the PEO processing of the Zr-Ti-Nb alloy. The present work concerns the surface modification of the Zr-Ti-Nb alloy by plasma electrolytic oxidation (PEO) to develop stable oxide coatings with enhanced functionality and bioactivity. The use of ethylenediaminetetraacetic acid (EDTA)-based electrolytes with an organic source of calcium provided repeatable conditions for the production of microporous PEO oxide coatings with a satisfactory level of incorporation of calcium, phosphorus, and amino groups. The PEO coatings were produced using the DC regime and the best current-voltage conditions for the oxidation were proposed. The morphology and chemical composition of the oxide coatings fabricated on the Zr-Ti-Nb alloy were investigated using scanning electron microscopy (SEM+EDS), X-ray diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). Uniform films with fine pore size and ZrO2 as the predominant oxide phase were formed. The oxide films showed superior corrosion resistance compared to the untreated Zr-Ti-Nb alloy. The results of the experiments indicate that this new alloy modified with the proposed PEO treatment shows potential for biomedical applications.