Application of coupled substrate aging and TiO2 nanotube crystallization heat treatments in cold-rolled Ti-Nb-Sn alloys

摘要

Among titanium alloys, the beta-type is the most indicated for orthopedic implants due to the reduced elastic modulus compared with alpha + beta alloys. To improve osseointegration, the growth of a self-ordered titania nanotube layer onto the surface of titanium alloy implant pieces is a strategy used to accelerate bone growth. In this paper, the effects of heat treatment for titania nanotube crystallization on Ti-Nb and Ti-Nb-Sn alloys on the phase transformation, the Vickers hardness, and the elastic modulus of the substrate were investigated. TiO2 layers were grown onto cold-rolled Ti alloy substrates by anodization, and crystallization to anatase was followed by glazing-angle high-temperature X-ray diffraction with a heating ramp of 288 K/min to 623 K, where the samples were held for up to 4 h. The dynamic of the alpha- and omega-phase formation/dissolution was followed by X-ray diffraction. Transmission electron microscopy was used to confirm the presence of the alpha- and omega-phases and their volumes and dimensions. As a result of the TiO2 crystallization heat treatment, a continuous increase in the hardness was observed for the Ti-35Nb and Ti-35Nb-2Sn alloys, which is attributed to dissolution of alpha aEuro(3) and the formation of omega precipitates. The same feature was observed for the elastic modulus. In the Ti-35Nb-4Sn alloy, the reverse decomposition of martensite resulted in the beta phase and later in alpha phase precipitation. The aging of this alloy resulted in a homogeneous distribution of a high volumetric fraction of fine and dispersed alpha phase, which resulted in a hardness increase from 220 to 270 HV. This coupled heat treatment resulted in high hardness, low elastic modulus, and a nanotube with an anatase crystal phase.