Effect of Nb addition on anodic behavior of Ti alloy in electrolyte containing calcium and phosphorus

The surface characteristics of the anodic oxide film (AOF) before and after dielectric breakdown on a Ti–30Nb–1Fe–1Hf alloy anodized in the electrolyte containing Ca and P were investigated. The AOF comprises an almost amorphous structure with local bubbles. The electrolyte-derived species are incorporated into the outer part of the AOF and stabilize the amorphous structure. Dielectric breakdown hardly affects the AOF composition, but it reduces the hydroxyl groups on the surface. Furthermore, Nb oxide can effectively hinder AOF rupture and increase the dielectric breakdown voltage of the AOF on Ti–30Nb–1Fe–1Hf compared with that of the AOF on pure Ti.