This study produced non-equiatomic TiNbZrTaMn and TiNbZrTaMo high entropy alloy (HEAs) by argon arc-melting and heat-treated for microstructural homogenization. The phase composition, microstructure, and selected mechanical properties were measured and compared with theoretical predictions. Additionally, electrochemical and cytotoxicity tests evaluated their potential applicability for use as biomaterials. X-ray diffraction measurements patterns showed a single BCC phase for the TiNbZrTaMn and a secondary HCP phase for the TiNbZrTaMo sample. The microstructural analysis revealed the formation of irregular grain boundaries and some lamellae formation, with chemical segregation of the alloying elements at the sub-micro-scale. The samples exhibited elastic modulus (80–110 GPa) closer to CP-Ti grade 2 (100 GPa) and higher Vickers microhardness (450–550 HV) than Ti–6Al–4V alloy (400 HV). The electrochemical and biological tests indicated a superior corrosion resistance against 0.9% NaCl solution compared with commercial metallic biomaterials, with proper cell adhesion and viability of pre-osteoblastic cells and hydrophilic behavior. Altogether, the data indicate that TiNbZrTaMn depicts better applicability potential for being used as a biomaterial in biomedical applications than some commercial materials (SS 316L, CP-Ti grade 2, and Ti–6Al–4V), mainly considering load-bearing orthopedical implants.

In this study, MAO treatment was used to enrich, with bioactive Ca, Mg and P atoms, as-casted and heat-treated Ti-15Zr-xMo (x = 0, 5, 10 and 15 wt%) alloys, for potential use as advanced metallic biomaterials. The chemical composition of the surface was evaluated by EDS and XPS measurements. The morphology and microstructure was analyzed by OM and SEM images. Crystalline structure and phase composition were characterized by XRD measurements. The results indicated that the oxide layers were porous, with microstructural features of the bulk (grain size and secondary phases) slightly affecting the surface characteristics (pore size, chemical and phase composition). The crystalline structure of the oxide layers were composed by a mixture of anatase and rutile phases (TiO2), with a minority of tetragonal zirconia (ZrO2) and traces of CaCO3 and P2O3 compounds. Chemical analysis indicated that the oxide layers were composed mainly by Ti and Zr oxides, with successful incorporation of the bioactive elements. The obtained results evidenced that the surface characteristics of MAO-treated Ti surfaces can be properly adjusted by the addition of alloying elements and implementation of specific heat treatments on the substrate. This finding can be quite useful for the development of novel biomedical implants.

This study evaluated the surface functionalization of a non-equiatomic TiZrNbTaMo high-entropy alloy (HEA) by micro-arc oxidation (MAO) in Cu-rich electrolytes to tailor its performance for biomedical implants. The Cu content was varied, and the resulting coatings were investigated for their morphology, phase constitution, chemical structure, wettability, and cytocompatibility. X-ray diffraction (XRD) measurements of the substrate indicated a body-centered cubic (BCC) matrix with minor HCP features, while the MAO-treated samples depicted amorphous halo with sparse reflections assignable to CaCO₃, CaO, and CaPO₄. Chemical spectroscopic analyses identified the presence of stable oxides (TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅, MoO₃) and the successful incorporation of bioactive elements (Ca, P, Mg) together with traces of Cu, mainly as Cu₂O. MAO treatment increased surface roughness and rendered a hydrophilic behavior, which are features typically favorable to osseointegration process. In vitro cytotoxic assays with MC3T3-E1 cells (24 h) showed that Cu addition did not induce harmful effects, maintaining or improving cell viability and adhesion compared to the controls. Collectively, MAO in Cu-rich electrolyte yielded porous, bioactive, and Cu-incorporated oxide coatings on TiZrNbTaMo HEA, preserving cytocompatibility and supporting their potential for biomedical applications like orthopedic implants and bone-fixation devices.