Microstructure and surface characteristics of hydroxyapatite coating on titanium and Ti-30Nb-1Fe-1Hf alloy by anodic oxidation and hydrothermal treatment

►The anodic oxide film(AOF) comprises crystalline particles in amorphous matrix. ►The AOF on Ti-Nb has a worse crystallinity than that on commercial pure Ti. ►The amorphous structure is beneficial for HA growth during hydrothermal treatment.