Microstructures and mechanical properties of anodic oxides on TiNbSn implant alloys

Abstract

This study explores the microstructure characteristics and mechanical properties of anodic oxides on the TiNbSn alloy (TNS) and compares them to those on pure Ti. After 90 s of anodization, spark discharge occurs in the TNS electrode, whereas pure Ti does not exhibit this phenomenon; instead, intense gas generation is observed at the electrode surface. The anodized TNS develops a rough and thick oxide with a dual-phase consisting of rutile and anatase TiO₂, with the rutile fraction increasing as anodization progresses. By contrast, anodized Ti forms a thin and glassy layer of anatase TiO₂ characterized by alternating low- and high-density pores in the cross-sectional direction, and the growth rate of anodized Ti is lower than that of anodized TNS. The surface roughness and surface area of the anodized oxides increase with anodization, with both the rate of increase and overall value being higher for anodized TNS as compared to anodized Ti. This vigorous chemical reaction in TNS is attributed to the fact that pentavalent Nb reacts more efficiently with oxygen ions than tetravalent Ti, resulting in the formation of an insulating oxide. Anodized TNS exhibits higher hardness and exfoliation strength than anodized Ti due to the presence of hard and strongly adhered rutile TiO₂. Potentiodynamic polarization measurements indicate that anodization significantly reduces the passivation current density of TNS as compared to Ti. It is proposed that anodizing reactions differ based on the valence of the Ti or Ti-alloy electrodes, highlighting anodization as an effective method for enhancing the hardness and corrosion resistance of TNS.