Porous nanocrystalline titania films by plasma electrolytic oxidation

Nanocrystalline titania films were prepared by plasma electrolytic oxidation of a titanium alloy at 200–350 V in a Na2CO3 electrolytic solution using a pulsed power supply. XRD, EDS and Field Emission (FE) SEM were employed to characterize the phase, composition, and microstructure of the films. Vickers indentation, nanoindentation and adhesion–tension test were used to evaluate the mechanical properties of the films. The phase, pore size and thickness of the films strongly depend on the applied voltage consistent with the previous reports. The films prepared at 350 V were porous with ∼1 μm pores and the pore walls were composed of 10–20 nm rutile crystallites. The hardness, Youngʹs modulus and bond strength of the film were 0.9±0.2 GPa, 32±4 GPa and 37±3 MPa, respectively. The film exhibited a significant plasticity and ductility compared to the conventional coarse-grained titania ceramics.