Effects of post-processing on microstructure and adhesion strength of TiO2 nanotubes on 3D-printed Ti-6Al-4V alloy

Abstract

Typical 3D-printing processes involve rapid cooling steps that significantly affect the mechanical behavior of printed Ti-6Al-4V alloys. In this study, the 3D-printing technique was used to fabricate Ti-6Al-4V parts, as is customary of bone implants; subsequently, the parts were heat-treated to improve the mechanical properties and the adhesion of surface TiO2 nanotubes arrays. One-step anodization was applied to the printed alloys to obtain surface TiO2 nanotubes arrays. This is the first study investigating the effects of heat treatment of 3D-printed Ti-6Al-4V alloys, both pre and post - anodization. The morphology of the TiO2 nanotube layers was characterized by optical microscopy (OM) and field emission scanning electron microscopy (FESEM); phases were confirmed by X-ray diffraction (XRD); adhesion of TiO2 nanotubes arrays was proved by scratch tests; hydrophilic properties were confirmed by water contact angle measurements. The results showed that samples heat-treated at 950 °C before anodization formed α and β structural phases, resulting in a peak-and-valley morphology in the TiO2 nanotube arrays. Sample annealing at 500 °C after anodization increased the inner diameter of the TiO2 nanotubes and improved the adhesion strength between the TiO2 nanotube arrays and the 3D-printed Ti-6Al-4V substrate. Moreover, annealed samples displayed lower water contact angles, signifying that the hydrophilicity is increase. These results suggest that a 3D-printed Ti-6Al-4V part with an added TiO2 nanotubes array may be suitable during the production of the customized implants.