Surface Modification of Multicomponent Ti-Ta-Zr-Nb Alloys by Plasma Electrolytic Oxidation

Quaternary β-Ti-xTa-xZr-xNb (TTZN) alloys (x = 10, 20, and 30 wt%) were surface-modified by plasma electrolytic oxidation (PEO) to improve their surface properties. This treatment promotes the incorporation of bioactive ions, such as Ca and P, and favors the formation of a porous anodic surface resulting from the oxidation of the precursor metals. This study investigated how the addition of alloying elements (Zr, Ta, and Nb) influences oxide formation, PEO-induced pore morphology, wettability, and coating hardness. The surfaces were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS), Vickers microhardness testing, and wettability analysis. XRD analysis revealed that the TTZN10 alloy exhibited crystalline TiO2 phases in the form of anatase and rutile. In contrast, the TTZN20 and TTZN30 alloys exhibited only cubic ZrO2 diffraction peaks, while no TiO2 peaks were detected within the detection limits of the XRD technique. Micrographs showed micrometric pores on all alloy surfaces. The TTZN20 alloy exhibited the highest porosity (31.8%), which correlated with lower hydrophilicity (θ = 79°) and high surface free energy (67 mJ/m2). After PEO treatment, all surfaces exhibited high hardness values ranging from 491 to 561 HV. The highest hardness was observed for TTZN10, attributed to the mixed anatase/rutile TiO2 phase composition.