Effects of substrate preparation on TiO2 morphology and topography during anodization of biomedical Ti6Al4V

TiO2 coatings were fabricated by anodizing unpolished and polished Ti6Al4V substrates in 1-3 M H2SO4 for 10 and 20 min at 120 V. Anatase was the principal polymorph and oxygen dissolution in the Ti6Al4V substrates caused alpha Ti lattice contraction. Dielectric breakdown and associated heating of the insulating TiO2 promoted trace rutile formation. The surface preparation of the Ti6Al4V substrates was the principal factor that determined not only the grain and pore sizes but also the morphology and topography of the coating. Consequently, the presence of the amorphous TiO2 passivating layer (unpolished) resulted in thicker and more irregular coatings than when anodization was done on the bare metal surface (polished). Large-scale delamination steps were observed for the coatings on the unpolished substrates while localized delaminations occurred for the coatings on polished substrates; the amounts of both increased with increasing anodization time. 3D laser scanning confocal microscopy allowed distinction between the fine-scale morphology and the coarse-scale topography. These data showed that increasing time and acid concentration resulted in similar trends of increasing roughness (morphology) and unevenness (topography). The present work focusses on the effect of initial substrate surface characteristics and its modification to improve the quality of the coatings formed by anodization of titanium biomedical implants.