Influence of microstructural features on the growth of nanotubular oxide layers on β-phase Ti-24Nb-4Zr-8Sn and α + β-phase Ti-13Nb-13Zr alloys

Abstract

Anodization of titanium alloys allows us to obtain nanotube oxide structures consisting of a mixture of oxides of alloying additives which might extend their scope of application and improve their surface properties. However, the complex microstructure of two-phase α + β Ti alloys presents a much greater influence on the homogeneity of nanotubular layers as compared to a single α-phase pure titanium. In this work, we analyzed how changes at the microstructural level (the amount, size or shape of the precipitates of individual phases) affect the growth of nanotubes on two biomedical alloys Ti-24Nb-4Zr-8Sn and Ti-13Nb-13Zr after different heat treatment. We found that morphology of nanotubular oxide layer imitate the microstructure of the substrate quite accurately what has been clearly seen especially for Ti-13Nb-13Zr alloy with a different size and morphology of α/α’ phase precipitates. The height of nanotubes was highly dependent on the β phase content, i.e. the higher the amount of the β phase, the higher the oxide nanotubes what is presumably due to the preferential growth of Nb 2 O 5 and ZrO 2 oxides. Moreover, the results showed that it is possible to fabricate crystalline nanotubes on the annealed Ti-13Nb-13Zr substrates immediately after the anodization process without a typical post-heat treatment. We suppose that this results from the presence of crystalline transition layer after initial heat treatment as well as internal stresses in the two-phase microstructure that induced the crystalline transformation. • NTs layers were fabricated on α + β-phase Ti alloys with various microstructure. • Morphology of layers imitated the size and shape of α/α’ phase precipitates. • The height of NTs grew with the higher amount of β phase. • Crystalline NTs were obtained on Ti-13Nb-13Zr without typical post-heat treatment.